#include<stdio.h>
#include<algorithm>
using namespace std;
int n,v[801];
int cautbin(int a)
{
	int pas=1<<9,i;
	for(i=0;pas;pas>>=1)
		if (i+pas<=n && v[i+pas]<=a)
			i+=pas;
	return i;
}
int main()
{
	freopen("nrtri.in","r",stdin);
	freopen("nrtri.out","w",stdout);
	int rez,i,j,k;
	scanf("%d",&n);
	for(i=1;i<=n;i++)
		scanf("%d",&v[i]);
	sort(v+1,v+n+1);
	rez=0;
	for(i=1;i<=n;i++)
		for(j=i+1;j<=n;j++)
		{
			k=cautbin(v[i]+v[j]);
			if(k>j) rez+=k-j;
		}
	printf("%d",rez);
	return 0;
}