#include <fstream>
#include <algorithm>

using namespace std;

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

int v[802];

int main()
{
    int n;
    fin >> n;
    for(int i = 0; i < n; i++)
        fin >> v[i];

    sort(v, v + n);
    int x1 = 0, x2 = 1, y = 2, rez = 0;

    while(y < n)
    {
        while(v[x1] + v[x2] >= v[y] && y < n)
            y++;
        rez += y - x2 - 1;
        if(x1 == x2 - 1 || v[x1 + 1] - v[x1] > v[x2 + 1] - v[x2])
            x2++;
        else
            x1++;
    }
    fout << rez;
    return 0;
}