#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;

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

const int L=9;
int n,v[801],x,y;


int cautbin(int x, int y )
{
    int r,pas;
    r=0;
    pas=1<<L;
    while(pas!=0)
    {
        if(r+pas<=n && v[r+pas]<=x+y)
        {
            r+=pas;
        }
        pas/=2;
    }
    //out << r << "\n";
    return r;
}

int main()
{
    int i,j,nr=0;
    in>>n;

    for(i=1; i<=n; i++)
    {
        in>>v[i];
    }
    sort(v,v+n+1);

    for(i=1; i<=n-1; i++)
    {
        for(j=i+1; j<=n; j++)
            nr+=cautbin(v[i],v[j])-j;
    }
    out<<nr;
    return 0;
}