#include <fstream>
#include <algorithm>

using namespace std;

const int NMAX = 800;
int v[NMAX + 1];

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

int main() {
    int n, st, dr, ans;
    
    fin >> n;
    for (int i = 1; i <= n; i++) 
        fin >> v[i];
    sort(v + 1, v + n + 1); // indexare de la 1

    ans = 0;
    for (int i = 1; i <= n - 2; i++) {
        st = dr = i + 1;
        while (st <= n - 1) {
            while (dr < n && v[dr + 1] <= v[i] + v[st])
                dr++;
            ans += dr - st;
            st++;
        }
    }
    fout << ans << "\n";
    return 0;
}