#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
int v[900];
int main(){
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);
    int n,i;
    cin >> n;
    for(i = 1 ; i <= n; i++){
        cin>> v[i];
    }
    int rez = 0,k,j;
    sort(v + 1, v + n + 1);
    for(i = 1; i <= n - 2; i++){
        k = i + 2;
        for(j = i + 1; j <= n - 1; j++){
            while(v[i] + v[j] >= v[k] && k != n + 1 ){
                ++rez;
                ++k;
            }
        }
    }
    cout<<rez;
}