# include <iostream>
using namespace std;

int main()
{
    int n;
    cin >> n;
    int a[105];
    for (int i = 1; i <= n; i++)
        cin >> a[i];
    int ans = 0;
    for (int i = 1; i <= n - 1; i++)
    {
        for (int j = i + 1; j <= n; j++)
        {
            for (int k = 1; k <= n; k++)
            {
                if (a[i] + a[j] == a[k])
                {
                    ans++;
                }
            }
        }
    }
    cout << ans << endl;
    return 0;
}

30分求助