#include <bits/stdc++.h>

using namespace std;

ifstream f("bete2.in");
ofstream g("bete2.out");

int main(void) {
    int a[3001], n = 0, count = 0, st = 0, dr = 0, x = 0;
    f >> n;
    for (int i = 1; i <= n; i++) f >> a[i];

    sort(a, a + n + 1);

    for (int i = n; i >= 3; i--) {
        x = a[i];
        st = 1, dr = i - 1;

        while (st < dr) {
            int sum = a[st] + a[dr];

            if (sum >= x){
                count++;
                st++;
                dr--;
            }
            else if (sum < x) st++;
            else dr--;
        }
    }
    g << count;
}