11681209

http://codeforces.net/problemset/problem/538/C

i have been stuck in this problem for like 2 days and i can't move to another one . i am so close . testcase wrong answer . wrong answer 1st words differ — expected: '219', found: '218' so annoying . :D

here is my code i hope you can help

include <bits/stdc++.h>

using namespace std;

int totaltime,n; pair < int , int > arr[100005];

int main() { scanf("%d %d",&totaltime,&n);

for(int i=1; i<=n; i++)
{
    cin>>arr[i].first;
    cin>>arr[i].second;
}
arr[0].first=arr[0].second=0;
int ans=0;
for(int i=1; i<=n; i++)
{
   // cout<<ans<<endl;
    if( abs(arr[i].second-arr[i-1].second) > abs(arr[i].first-arr[i-1].first)&&i!=1)
    {
     //   cout<<i<<endl;
        cout<<"IMPOSSIBLE\n";
        return 0;
    }
    else
        {
            //if((abs(arr[i].first-arr[i-1].first)%2==0))ans= max (ans, ((abs(arr[i].first-arr[i-1].first) - abs(arr[i].second-arr[i-1].second))/2) + arr[i-1].second );

            ans= max (ans, ((abs(arr[i].first-arr[i-1].first) - abs(arr[i].second-arr[i-1].second))/2) + arr[i-1].second );
        }

}

// cout<<ans<<endl; ans=max(ans,arr[n].second+totaltime-arr[n].first); cout<<ans<<endl;

return 0;

}