First problem — task rejections. 300iq rejected about 13 problems, 6 of which were supposed to be problem D. In the end, we came up with E, and the old E moved to D.

These are the verdicts with which the problems were rejected:

1. The idea is very simple here and the implementation is very simple too, this problem is definitely not D1C-D and definitely not interesting.
2. Not an interesting problem, too standard, without new ideas.
3. This is a known problem which is solved quite simply by a compressed tree.
4. Unfortunately, it seems to me that this problem does not fit D1B. It is a funny construct but it is too technical (not interesting enough) for this position and too simple for the next ones.
5. This problem is solved very simply by taking a close look at the sequence, so it is not very interesting.
6. It seems to me that this problem is too standard. It is as if in the condition it is written, which dp should be written.
7. The idea of 4 consecutive numbers is known.
8. It's a known problem.
9. It's a known problem.
10. It's too standard.
11. There's some greed in there. Is that the right thing to do?
12. Well, first of all, it's doubtful you have any proof. Second of all, isn't that on oeis?
13. It doesn't make her any better, it's a known problem.

When the problems were already formed, their creation began. In some problems, it was necessary to lower the constraints, which made it impossible to cut off some non-deterministic or not optimal solutions.

Otherwise, everything was fine until the last 18 hours before the contest began...

• Mike MikeMirzayanov Mirzayanov sent 7 issues to problem A. It was necessary to redo all the tests in the problem and much more.
• While we were correcting them, coordinator Ildar 300iq Gainullin told us to remove all the illustrations for the problem (memes and just cool pictures at the bottom of the notes). We did not like it very much, we wanted the pictures to be included in the contest.
• We finished fixing problem A, and went to bed. At that time Ildar (thank him very much) was polishing the conditions of all the other problems. Unfortunately, at that moment he removed the pictures. He also suddenly renamed problem F and city in the English version of problem D.
• 4 hours before the beginning. Mikhail Mirzayanov started sending issues to other problems.
• We had to redo almost all the tests for problems B, C and D.
• Heroically won the limits in E 2 hours before the contest start.

A total of 475 commits to the Polygon were made.

During the round there were many of the same type, but also some funny clares. For example:

• Problem C. i cant solve it
• Problem E. When will a COVID 19 vaccine come out???

Thanks to everyone who upvotes this editorial!

#include <iostream>

using namespace std;

int main() {
    int t, n, m;
    cin >> t;
    while (t--) {
        cin >> n >> m;
        cout << (n * m + 1) / 2 << '\n';
    }
}

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

void solve() {
    int n;
    cin >> n;
    vector<int> arr(n);
    for (int &el : arr)
        cin >> el;
    sort(arr.begin(), arr.end());
    for (int i = n - 1; i >= 0; i--) {
        if (arr[i] <= i + 1) {
            cout << i + 2 << '\n';
            return;
        }
    }
    cout << 1 << '\n';
}

int main() {
    int t;
    cin >> t;
    while (t--)
        solve();
}

#include <iostream>

using namespace std;

int main() {
    int t;
    cin >> t;
    while (t--) {
        long long a, b, c, d;
        cin >> a >> b >> c >> d;
        cout << (c - a) * (d - b) + 1 << '\n';
    }
}

#include <iostream>
#include <algorithm>
#include <vector>

#define int long long

using namespace std;

signed main() {
  int n, len;
  cin >> n >> len;
  vector<int> A(2 * n);
  for (int i = 0; i < n; i++) {
    cin >> A[i];
    A[n + i] = A[i];
  }
  n *= 2;
  
  vector<int> B = {0}, C = {0};
  for (int i = 0; i < n; i++) 
    B.push_back(B.back() + A[i]);
  for (int i = 0; i < n; i++) 
    C.push_back(C.back() + (A[i] * (A[i] + 1)) / 2);
  int ans = 0;
  for (int i = 0; i < n; i++) {
    if (B[i + 1] >= len) {
      int z = upper_bound(B.begin(), B.end(), B[i + 1] - len) - B.begin();
      int cnt = C[i + 1] - C[z];
      int days = B[i + 1] - B[z];
      int too = len - days;
      cnt += ((A[z - 1] * (A[z - 1] + 1)) / 2);
      cnt -= (((A[z - 1] - too) * (A[z - 1] - too + 1)) / 2);
      ans = max(ans, cnt);
    }
  }
  cout << ans;
}

#include <iostream>
#include <vector>

using namespace std;

#define int long long

signed main() {
  int n;
  cin >> n;
  int N = (n + 1) / 2;
  vector<int> a(N);
  for (int &el : a)
    cin >> el;
  int Ax;
  cin >> Ax;
  vector<int> m(N + 1, 0);
  int Pprefsm = 0;
  for (int i = 1; i < N + 1; ++i) {
    Pprefsm += Ax - a[i - 1];
    m[i] = min(m[i - 1], Pprefsm);
  }
  int Aprefsm = 0;
  for (int k = 1; k <= N; ++k)
    Aprefsm += a[k - 1];
  for (int k = N; k <= n; ++k) {
    if (Aprefsm + m[n - k] > 0)
      return cout << k, 0;
    Aprefsm += Ax;
  }
  cout << -1;
}

#include <bits/stdc++.h>

using namespace std;

#define int long long
const int LIM = 2e5;

bool is_increasing(const vector<int> &vec) {
  for (int i = 0; i < vec.size() - 1; i++) {
    if (vec[i] >= vec[i + 1])
      return false;
  }
  return true;
}

bool is_decreasing(const vector<int> &vec) {
  for (int i = 0; i < vec.size() - 1; i++) {
    if (vec[i] <= vec[i + 1])
      return false;
  }
  return true;
}

vector<int> rollback(const vector<int> &vec) {
  vector<int> ans(vec.size());
  ans[0] = vec[0];
  for (int i = 1; i < vec.size(); i++)
    ans[i] = vec[i] - vec[i - 1];
  return ans;
}

signed main() {
  int n;
  cin >> n;
  vector<int> a(n), b(n);
  for (int &i : a)
    cin >> i;
  for (int &i : b)
    cin >> i;
  vector<int> a_rev = a;
  reverse(a_rev.begin(), a_rev.end());

  if (n == 1) {
    if (a == b)
      cout << "SMALL" << '\n' << 0 << '\n';
    else
      cout << "IMPOSSIBLE" << '\n';
    return 0;
  }

  int sum_a = accumulate(a.begin(), a.end(), 0LL);
  int sum_b = accumulate(b.begin(), b.end(), 0LL);
  int rollback_cnt = 0;

  if (n == 2) {
    vector<int> ans; // -1 = R, X = PPP..PP (x times)
    int move_cnt = 0, roll_cnt = 0;  // both types

    bool rev = a[0] > a[1];
    if (rev)
      swap(a[0], a[1]);

    if (b[0] > b[1]) {
      swap(b[0], b[1]);
      ans.push_back(-1);
      move_cnt++;
    }
    while (true) {
      if (sum_a > sum_b) {
        cout << "IMPOSSIBLE" << '\n';
        return 0;
      }

      if (sum_a == sum_b) {
        if (a != b) {
          cout << "IMPOSSIBLE" << '\n';
          return 0;
        }

        if (rev) {
          ans.push_back(-1);
          move_cnt++;
        }

        if (rollback_cnt > LIM) {
          cout << "BIG" << '\n' << rollback_cnt << '\n';
          return 0;
        } else {
          cout << "SMALL" << '\n' << move_cnt << '\n';
          reverse(ans.begin(), ans.end());
          for (auto i : ans) {
            if (i == -1)
              cout << "R";
            else {
              for (int _ = 0; _ < i; _++)
                cout << "P";
            }
          }
          cout << '\n';
          return 0;
        }
      }

      if (a[0] == b[0]) {
        if ((b[1] - a[1]) % b[0] == 0) {
          roll_cnt = (b[1] - a[1]) / b[0];
          ans.push_back(roll_cnt);
          move_cnt += roll_cnt, rollback_cnt += roll_cnt;
          b = a;
          sum_b = b[0] + b[1];
        } else {
          cout << "IMPOSSIBLE" << '\n';
          return 0;
        }
      } else {
        roll_cnt = b[1] / b[0];
        ans.push_back(roll_cnt);
        move_cnt += roll_cnt, rollback_cnt += roll_cnt;

        ans.push_back(-1);
        move_cnt++;
        swap(b[0], b[1]);
        b[0] %= b[1];
        sum_b = b[0] + b[1];
      }
    }
  }

  string ans;

  while (true) {
    if (sum_a == sum_b) {
      if (a_rev == b) {
        ans.push_back('R');
        reverse(b.begin(), b.end());
      }
      if (a == b) {
        reverse(ans.begin(), ans.end());
        if (rollback_cnt > LIM)
          cout << "BIG" << '\n' << rollback_cnt << '\n';
        else
          cout << "SMALL" << '\n' << ans.size() << '\n' << ans << '\n';
      } else
        cout << "IMPOSSIBLE" << '\n';
      return 0;
    } else if (is_increasing(b)) {
      b = rollback(b);
      sum_b = accumulate(b.begin(), b.end(), 0LL);
      ans += 'P';
      rollback_cnt++;
    } else if (is_decreasing(b)) {
      reverse(b.begin(), b.end());
      ans += 'R';
    } else {
      cout << "IMPOSSIBLE" << '\n';
      return 0;
    }
  }
}

#include <bits/stdc++.h>

using namespace std;
#define int long long

signed main() {
  int n;
  cin >> n;
  vector<int> a(n), b(n);
  for (int i = 0; i < n; ++i) cin >> a[i];
  for (int i = 0; i < n; ++i) cin >> b[i];
  if (n == 1) {
    if (a[0] == b[0]) cout << "SMALL\n" << 0;
    else cout << "IMPOSSIBLE";
    return 0;
  }
  if (n == 2) {
    vector<pair<int, bool>> res;
    int kol = 0;
    while (true) {
      if (b[0] == 0 || b[1] == 0) {
        cout << "IMPOSSIBLE";
        return 0;
      }
      if (a == b) break;
      if (a[0] == b[1] && a[1] == b[0]) {
        res.emplace_back(1, false);
        break;
      }
      if (b[0] == b[1]) {
        cout << "IMPOSSIBLE";
        return 0;
      }
      if (b[0] > b[1]) {
        res.emplace_back(1, false);
        swap(b[0], b[1]);
      }
      if (a[0] == b[0] && a[1] < b[1] && a[1] % b[0] == b[1] % b[0]) {
        res.emplace_back((b[1] - a[1]) / b[0], true);
        kol += res.back().first;
        break;
      }
      if (a[1] == b[0] && a[0] < b[1] && a[0] % b[0] == b[1] % b[0]) {
        res.emplace_back((b[1] - a[0]) / b[0], true);
        kol += res.back().first;
        res.emplace_back(1, false);
        break;
      }
      kol += b[1] / b[0];
      res.emplace_back(b[1] / b[0], true);
      b[1] %= b[0];
    }
    if (kol > 2e5) {
      cout << "BIG\n";
      cout << kol;
    } else {
      cout << "SMALL\n";
      int flex = 0;
      for (auto i : res) flex += i.first;
      cout << flex << "\n";
      for (int i = res.size() - 1; i >= 0; --i) {
        for (int j = 0; j < res[i].first; ++j) {
          if (res[i].second) cout << "P";
          else cout << "R";
        }
      }
    }
    return 0;
  }
  vector<bool> ans;
  int kol = 0;
  while (true) {
    if (a == b) break;
    reverse(b.begin(), b.end());
    if (a == b) {
      ans.push_back(false);
      break;
    }
    reverse(b.begin(), b.end());
    bool vozr = false, ub = false, r = false;
    for (int i = 1; i < n; ++i) {
      if (b[i] > b[i - 1]) vozr = true;
      else if (b[i] < b[i - 1]) ub = true;
      else r = true;
    }
    if (r || (vozr && ub)) {
      cout << "IMPOSSIBLE";
      return 0;
    }
    vector<int> c(n);
    if (ub) {
      ans.push_back(false);
      reverse(b.begin(), b.end());
    }
    c[0] = b[0];
    for (int i = 1; i < n; ++i) {
      c[i] = b[i] - b[i - 1];
    }
    ans.push_back(true);
    b = c;
    ++kol;
  }
  if (kol > 2e5) {
    cout << "BIG\n" << kol;
  } else {
    cout << "SMALL\n" << ans.size() << "\n";
    for (int i = ans.size() - 1; i >= 0; --i) {
      if (ans[i]) cout << "P";
      else cout << "R";
    }
  }
}