#include<stdio.h>
#include<algorithm>
using namespace std;
int lat[801];
int main(){
	freopen("nrtri.in","r",stdin);
	freopen("nrtri.out","w",stdout);
	int n,i,j,s,u;
	scanf("%d",&n);
	for(i=0;i<n;i++)
		scanf("%d",&lat[i]);
	sort(lat,lat+n);
	
	s=0;
	for(i=0;i<n-2;i++){
		u=i+2;
		for(j=i+1;j<n-1;j++){
			while((lat[i]+lat[j]>=lat[u])&&(u<n))
				u++;
			s=s+u-j-1;
		}
	}
	
	printf("%d\n",s);
	return 0;
}