#include <iostream>
int main()
{
    using namespace std;
    int n;
    cin >> n;
    int* p = new int[n];
    int sum = 0;
    int a;
    for (int i = 0; i < n; i++)
        cin >> p[i];
    for (int i = 0; i < n; i++)
    {
        for (int j = i + 1; j < n; j++)
        {
            for (int l = 0; l < n; l++)
            {
                a = p[i] + p[j];
                if (a == p[l])
                    sum++;
            }
        }
    }
    cout << sum;
    delete[] p;
    return 0;
}