#include<stdio.h>
int i,j,k,n,a[801],nr,sum1,sum2,sum3;
int main(){
	freopen("nrtri.in","r",stdin);
	freopen("nrtri.out","w",stdout);
	scanf("%d",&n);
	for (i=1; i<=n; ++i) scanf("%d",&a[i]);
	for (i=1; i<=n-2; ++i)
		for (j=i+1; j<=n-1; ++j)
			for (k=j+1; k<=n; ++k)
			{
				sum1=a[i]+a[j];
				sum2=a[j]+a[k];
				sum3=a[i]+a[k];
				if (sum1>=a[k] && sum2>=a[i] && sum3>=a[j]) nr++;
			}
	printf("%d",nr);
	return(0);
}