#include <fstream>
#include <algorithm>

using namespace std;

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

int v[803], n;

int caut(int value, int l, int r) {
    int ans = l - 1;

    while (l <= r) {
        int m = (l + r) >> 1;
        if (v[m] <= value) {
            ans = m;
            l = m + 1;
        } else {
            r = m - 1;
        }
    }

    return ans;
}

int main()
{
    int ct = 0;

    fin >> n;

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

    sort(v + 1, v + n + 1);

    for(int i = 1; i < n - 1; i++) {
        for(int d = i + 1; d < n; d++) {
            ct += caut(v[i] + v[d],d + 1, n) - d;
        }
    }

    fout << ct;

    return 0;
}