#include <fstream>
#include <algorithm>
using namespace std;

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

const int NMAX = 803;

int v[NMAX], n, cnt;

int binary_search(int l, int r, int val)
{
	int ind = l - 1;

	while (l <= r)
	{
		int m = ((l + r) >> 1);
		if (v[m] <= val)
		{
			ind = m;
			l = m + 1;
		}
		else r = m - 1;
	}
	return ind;
}

int main()
{
	fin >> n;
	
	for (int i = 1; i <= n; ++i)
		fin >> v[i];

	sort(v + 1, v + n + 1);
	
	for (int i = 1; i < n; ++i)
		for (int j = i + 1; j <= n; ++j)
			cnt += binary_search(j + 1, n, v[i] + v[j]) - j;
		
	fout << cnt << "\n";

	return 0;
}