#include<bits/stdc++.h> using namespace std; int a[110]; bool vis[110]; int main(){ freopen("sum.in", "r", stdin); freopen("sum.out", "w", stdout); int n; cin >> n; int g = 0; for (int i = 0;i < n;i++){ cin >> a[i]; } for (int i = 0;i < n;i++){ for (int j = i+1;j < n;j++){ for (int k = 0;k < n;k++){ if (i != k && k != j){ if (a[i] + a[j] == a[k] && !vis[k]){ vis[k] = true; g++; } } } } } cout << g; return 0; }