#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cmath>
using namespace std;

int main() {
    int n; scanf("%d", &n);
    int a[111] = { 0 }; int cnt = 0;
    for (int i = 0; i < n; i++)
        scanf("%d", &a[i]);
    for (int i = 0; i < n; i++) {
        int flag = 0;
        for (int j = i + 1; j < n; j++) { 
            for (int k = 0; k < n; k++) {
                if (flag==0 && a[i] == a[j] + a[k]) {
                    cnt++;
                    flag = 1;
                }
            }
        }
    }
    printf("%d", cnt);
    return 0;
}