For convenience, I assume $$$L_i < R_i$$$

#include <bits/stdc++.h>
using namespace std;

int main() {
  cin.tie(0)->sync_with_stdio(0);
  
  int N;
  cin >> N;
  
  vector<pair<int, int>> ranges(N);
  for (auto &[L, R] : ranges) {
    cin >> L >> R;
  }
  
  vector<int> cc;
  for (auto [L, R] : ranges) {
    cc.push_back(L);
    cc.push_back(R);
  }
  sort(cc.begin(), cc.end());
  for (auto &[L, R] : ranges) {
    L = lower_bound(cc.begin(), cc.end(), L) - cc.begin();
    R = lower_bound(cc.begin(), cc.end(), R) - cc.begin();
  }
  
  sort(ranges.begin(), ranges.end(), [&](auto a, auto b) {
    return a.second - a.first < b.second - b.first;
  });
  vector<vector<pair<int, int>>> by_L(cc.size());
  vector<int> dp(cc.size());
  auto solve = [&](int L, int R) -> int {
    fill(dp.begin(), dp.end(), 0);
    for (int i = L; i < R; i++) {
      for (auto [Rj, dpj] : by_L[i]) {
        dp[Rj] = max(dp[Rj], dp[i] + dpj);
      }
      dp[i + 1] = max(dp[i + 1], dp[i]);
    }
    return dp[R];
  };
  for (auto [L, R] : ranges) {
    by_L[L].push_back({R, solve(L, R) + 1});
  }
  cout << solve(0, cc.size() - 1);
}