#include<bits/stdc++.h>
using namespace std;

int n, a[801];

int Search(int l, int r, int v)
{
    int m;

    while (l <= r)
    {
        m = (l + r) / 2;

        if (a[m] == v)
            return v;
        else
        {
            if(a[m] > v)
                r = m - 1;

            else
                l = m + 1;
        }
    }
    return -1;
}

int main()
{
    ifstream fin("nrtri.in");
    ofstream fout("nrtri.out");

    int n, cnt = 0;

    fin >> n;

    for(int i = 1; i <= n; ++i)
        fin >> a[i];

    for(int i = 1; i <= n; ++i)
        for(int j = 1; j <= n; ++j)
            if(i != j && Search(1, n, a[i] + a[j]) >= a[i] + a[j])
                cnt++;

    fout << cnt;

    return 0;
}