#include <fstream>
#include <stdio.h>
#include <algorithm>
#define dim 801
using namespace std;

int v[dim];
int binsearch( int st, int dr, int val) {
    int mid = (st + dr ) / 2;

    if (st == dr) {
        return st;
    }

    if (v[mid] > val) {
        return binsearch(st, mid, val);
    } else {
        return binsearch(mid + 1, dr, val);
    }
}

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

    int n,nr = 0;

    fin >> n;

    for (int i = 0; i < n; i++) {
        fin >> v[i];
    }

    sort(v, v + n);

    for (int i = 0; i < n - 2; i++) {
        for (int j = i + 1; j < n - 1; j++) {
            int poz = binsearch(j, n - 1, v[i] + v[j]);

            nr += poz - j;
        }
    }

    fout << nr;

    fin.close();
    fout.close();
    return 0;
}