#include <bits/stdc++.h>
using namespace std;
int n,a[110];
int ret = 0;

int main(){
    cin >> n;
    for(int i = 1;i <= n;i++) cin >> a[i];
    for(int i = 1;i <= n;i++) {
        for(int j = i;j <= n;j++){
            if(i == j) continue;
            for(int k = 1;k <= n;k++){
                if(a[i] + a[j] == a[k]) ret++;
            }
        }
    }
    cout << ret;
    return 0;
}