#include <bits/stdc++.h>
using namespace std;
int main(){
  int n , sum = 0;
  cin >> n;
  int num[n + 1];
  for (int i = 1;i <= n;i++)
    cin >> num[i];
  sort (num + 1, num + n + 1);
  for (int i = 1;i <= n;i++)
    for (int j = i + 1;j <= n;j++)
      for (int k = j + 1;k <=n;k++){
        if ((num[i] + num[j]) == num[k]) sum ++;
        // cout << "i,j,k" << i << ' ' << j << ' ' << k << "\n";
      }
  cout << sum << "\n";
  return 0;
}

不知道问题出在了哪...哪位大佬能指点迷津...