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

using namespace std;

const int NMAX=800;
int c[NMAX + 1];

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

int n;
int sumfind(int x){
    int mij, st=1, dr=n+1;
    while (st<dr-1){
        mij=(st+dr)/2;
        if(c[mij]>x){
            dr=mij;
        }
        else{
            st=mij;
        }
    }
    return st;
}

int main()
{
    int i, j, sum, sumt=0;
    fin >> n;
    for (i=1;i<=n;i++){
        fin >> c[i];
    }
    sort (c+1,c+n+1);
    for (i=1;i<n-1;i++){
        for (j=i+1;j<n;j++){
            sum=(sumfind(c[i]+c[j]))-j;
            sumt= sumt + sum;
           // fout << sumt+sum << " ";
        }
    }
    fout << sumt;
}