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

using namespace std;

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

int n, v[801];

int cautbin(int x, int y){
    int r=0, pas;
    pas=1<<14;
    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;
}