#include <iostream>
#include <fstream>
#include <iomanip>
#include <algorithm>

using namespace std;

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

int x[801];
int n, m, st, dr, i, j, dif, s, sol;

int main()
{
    fin>>n;
    for(i=1; i<=n; ++i) fin>>x[i];
    sort(x+1, x+n+1);
    for(i=1; i<n-1; ++i)
    {
        for(j=i+1; j<n; ++j)
        {
            s=x[i]+x[j];
            st=j+1; dr=n;
            while(st<=dr)
            {
                m=(st+dr)/2;
                if(s>=x[m]) st=m+1;
                else dr=m-1;
            }
            sol=sol+dr-j;
        }
    }
    fout<<sol<<"\n";
    return 0;
}