#include <iostream>
#include <algorithm>
#include <fstream>
using namespace std;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
int n, a[801];
int cautbin(int x)
{
    int p = 1, u = n, poz = 0;
    while(p <= u)
    {
        int mij = (p + u) / 2;
        if(a[mij] <= x)
        {
            poz = mij;
            p = mij + 1;
        }
        else
            u = mij - 1;
    }
    return poz;
}
int main()
{int p,s=0,k;
    f >> n;
    for(int i = 1; i <= n; i++)
        f >> a[i];
    sort(a+1,a+n+1);
    for(int i = 1; i < n; i++)
        for(int j = i + 1; j <= n; j++)
        {
            p = cautbin(a[i] + a[j]);
            s += p - j;
        }
        g<<s;
    return 0;
}