#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
int n,v[900],nr;
int main()
{
    f>>n;
    for(int i = 0;i<n;i++)
        f>>v[i];
    sort(v,v+n);
    int i,j,k;
    for(i = 0;i <= n-3;i++)
    {
        j = i+1;
        k = n-1;
        while(v[i]+v[j]<=v[k] && k!=j)
        {
            k--;
            nr++;
        }
    }
    g<<nr;
    f.close();
    g.close();
    return 0;
}