#include <stdio.h>
#include <stdlib.h>

int n,a[802],sum=0;


int compare (const void * a, const void * b)
{
  return ( *(int*)a - *(int*)b );
}


void bs(int lo,int p){
int hi=n,mid,er=lo-1;

while(lo<hi){
mid=lo+(hi-lo+1)/2;

if(a[mid]<=p){lo=mid;}
else{hi=mid-1;}

}

if(a[lo]<=p){sum+=lo-er;}

}

int main(){
	freopen("nrtri.in","r",stdin);
	freopen("nrtri.out","w",stdout);
	int i,j;
	scanf("%d",&n);
	for(i=1;i<=n;i++){scanf("%d",&a[i]);}
	
	qsort (a, n, sizeof(int), compare);
	
	for(i=1;i<=n-2;i++)
		for(j=i+1;j<=n-1;j++)
			bs(j+1,a[i]+a[j]);

		printf("%d",sum/2);


	return 0;}