#include<stdio.h>
#include<algorithm>
using namespace std;
int a[805];
int bs(int st,int dr,int val)
{
	int med,last=0;
	while(st<=dr)
	{
		med=(st+dr)/2;
		if(a[med]<=val) {last=med;st=med+1;}
		else
			dr=med-1;
	}
	return last;
}
int main()
{
	freopen("nrtri.in","r",stdin);
	freopen("nrtri.out","w",stdout);
	int n,i,j,ind,nr=0;
	scanf("%d",&n);
	for(i=1;i<=n;i++)
		scanf("%d",&a[i]);
	sort(a+1,a+n+1);
	for(i=1;i<=n;i++)
		for(j=i+1;j<=n;j++)
		{
			ind=bs(j+1,n,a[i]+a[j]);
			if(ind) nr=nr+ind-j;
		}
	printf("%d\n",nr);
	return 0;
}