optimized

#include <iostream>
#include <vector>
using namespace std;

int main()
{
   int N, a;
   int buf_sum = 0;
   int m = 0;
   vector<int> array(5,0);
   cin >> N;
   for (int i=0; i< 5; i++){
       cin >> a;
       array[i] = a;
       m = m + a;
   }
   buf_sum = m;
   a = 0;
   for (int i=5; i< N; i++){
       buf_sum = buf_sum - array[0];
     for (int j=0; j<4; j++){
         array[j] = array [j + 1];
     }
     cin >> a;
     buf_sum = buf_sum + a;
     array [4] = a;
     if (buf_sum > m){
     m = buf_sum;
     }
   }
   cout << m;
    return 0;
}