#include <stdio.h>
#include <algorithm>
using namespace std;

int n, v[801];
 
int binary_search(int val)
{
    int i, step;
    for (step = 1; step <n; step <<= 1);
    for (i = 0; step; step >>= 1){
        if (i + step <= n && v[i + step] <= val){
           i += step;
		}
	}
    return i;
}

int main()
{
	freopen("nrtri.in","r",stdin);
	freopen("nrtri.out","w",stdout);
	scanf("%d",&n);
	int j;
	for(j=1;j<=n;j++){
		scanf("%d",&v[j]);
	}
	sort(v+1,v+n+1);
	int m,a,s=0;
	for(j=1;j<n-1;j++){
		for(m=j+1;m<n;m++){
			a=binary_search(v[j]+v[m])-m;
			s=s+a;
		}
	}
	printf("%d",s);
	return 0;
}