#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int n,v[1005],i,j,k,nr;
int main()
{
    fin>>n;
    for (i=1;i<=n;i++)
        fin>>v[i];
    sort(v+1,v+n+1);
    for (i=1;i<=n-2;i++)
    {
        for (j=i+1;j<=n-1;j++)
        {
            k=j+1;
            while (v[i]+v[j]>=v[k] && k<=n)
            {
                k++;
            }
            nr+=k-j-1;
        }
    }
    fout<<nr;
    return 0;
}