#include<stdio.h>
#include<algorithm>
using namespace std;
int v[801],n,num,k,i,j,l;

bool cmp(int x,int y)
{
	return x<y;
}


int main()
{
	freopen("nrtri.in","r",stdin);
	freopen("nrtri.out","w",stdout);
	scanf("%d",&n);
	for(i=1;i<=n;i++)
		scanf("%d",&v[i]);
	sort(&v[1],&v[n+1],cmp);
	l=n-2;
	for(i=1;i<=l;++i)
	{
		for(j=i+1,k=i+2;j<n;++j)
		{
			for(;k<=n&&v[i]+v[j]>=v[k];k++);
			num+=k-j-1;
		}
	}
	printf("%d",num);
	return 0;
}