#include <fstream>
#include <algorithm>

using namespace std;

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

int n, i, x, j, v[801], nr;

int main()
{   f >> n;
    for ( i = 1; i <= n; i++ ){
        f >> v[i];
    }
    sort ( v + 1, v + n + 1 );
    g << "\n";
    for ( i = 1; i <= n - 2; i++ ){
        for ( j = i + 1; j <= n - 1; j++ ){
            x = upper_bound ( v + 1, v + n + 1, v[i] + v[j] ) - v;
            nr = nr + x - j - 1;
        }
    }
    g << nr;



    return 0;
}