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

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

int n, v[801];

int cautare_binara(int x, int st, int dr){
    if(st <= dr){
        int m = (st + dr) / 2;
        if(x == v[m]) return m;
        else if(x < v[m]) return cautare_binara(x, st, m - 1);
        else return cautare_binara(x, m + 1, dr);
    }
    if(dr == -1)return 0;
    return dr;
}

int main()
{
    int i, j, k, sol = 0;
    fin>>n;
    for(i = 1; i <= n; ++i){
        fin>>v[i];
    }
    sort(v + 1, v + n + 1);
    for(i = 1; i <= n - 2; ++i){
        for(j = i + 1; j <= n - 1; ++j){
            k = cautare_binara(v[i] + v[j], j + 1, n);
            sol += k - j;
        }
    }
    fout<<sol;
    return 0;
}