#include <cstdio>
using namespace std;

const int Nmax = 801;

int main() {
    int n, x, i, j, st, dr, m;
    int v[Nmax];

    freopen("nrtri.in", "r", stdin);
    freopen("nrtri.out", "w", stdout);

    scanf("%d", &n);
    for (i = 1; i <= n; ++i) {
        scanf("%d", &x);
        for (j = i-1; x < v[j] && j > 0; --j) {
            v[j+1] = v[j];
        }
        v[j+1] = x;
    }

    for (x = 0, i = 1; i <= n-2; ++i) {
        for (j = i+1; j <= n=1; ++j) {
            st = j+1;
            dr = n;
            while (dr >= st) {
                m = (st+dr)/2;
                if (v[i]+v[j] >= v[m]) {
                    ++x;
                    st = m+1;
                } else {
                    dr = m-1;
                }
            }
        }
    }

    printf("%d\n", x);

    return 0;
}