#include <iostream>
#include <fstream>
#include <algorithm>
#define MAX 1000001

using namespace std;

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

int a[MAX], n, nr = 0;

bool ok(int a, int b, int c) {
	if (a + b >= c && a + c >= b && c + b >= a)return true;
	else return false;
}



int main() {
	in >> n;
	for (int i = 1; i <= n; i++) {
		in >> a[i];
	}
	sort(a, a + n + 1);
	for (int i = 1; i < n; i++) {
		for (int j = i + 1; j <= n; j++) {


				int left = j + 1, right = n, sol = -1;
				while (left <= right) {
					int mid = (left + right) / 2;
					if (a[mid] <= a[i] + a[j]) {
						left = mid + 1;
						sol = mid;
					}
					else {
						right = mid - 1;
					}

					if (sol != -1) nr += (sol - j);

				}


		}
	}
	out << nr - 1;
}