#include<bits/stdc++.h>
#define N 805
int n, l[N], i, j, k, nr;
int main()
{
	nr = 0;
	freopen("nrtri.in", "r", stdin);
	freopen("nrtri.out", "w", stdout);
	scanf("%d", &n);
	for(i = 1; i <= n; i++) scanf("%d", &l[i]);
	for(i = 1; i <= n-2; i++)
	 for(j = i+1; j <= n-1; j++)
	   for (k = j + 1; k <= n && l[i]+l[j] >= l[k]; k++)
	     nr++;
	printf("%d", nr);
	return 0;
}