#include <fstream>
#include <algorithm>

using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int v[800];
int cautare(int x, int st, int dr) {
	int mid;
	while (st < dr) {
		mid = st + (dr - st) / 2;
		if (v[mid] <= x)
			st = mid + 1;
		else
			dr = mid;
	}
	return st - 1;
}
int main() {
	int n, i, j, poz, cnt;
	fin >> n;
	for (i = 0; i < n; i++)
		fin >> v[i];
	sort(v, v + n);
	cnt = 0;
	for (i = 0; i < n - 1; i++) {
		for (j = i + 1; j < n; j++) {
			cnt += cautare(v[i] + v[j], j + 1, n) - j;
		}
	}
	fout << cnt;
	return 0;
}