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

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

int v[801],L=10;

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

int main()
{
    int n,i,j,nr=0,s;
    f>>n;
    for ( i=1 ; i<=n ; i++ )
        f>>v[i];

    sort ( v+1 , v+n+1 );

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