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

using namespace std;

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

const int L = 14;

int n,v[801],x,y;

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