#include <fstream>
#include <algorithm>

using namespace std;

const int NMax = 810;
int N;
int a[NMax];

int main()
{
    ifstream f ("nrtri.in");
    f >> N;
    for (int i = 1; i <= N; ++ i)
        f >> a[i];
    f.close();

    sort(a+1, a+N+1);

    int ans = 0;
    for (int i = 1; i <= N; ++ i)
        for (int j = i + 1; j <= N; ++ j)
            ans += (int)(upper_bound(a+j+1, a+N+1, a[i]+a[j]) - (a+j+1));

    ofstream g ("nrtri.out");
    g << ans << "\n";
    g.close();
    return 0;
}