#include <stdio.h>

FILE *f,*g;

int n,v[801],i,j,x,y,m,k;

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]);
 for (i=1;i<=n-1;i++)
  for (j=i+1;j<=n;j++)
	if (v[i]>v[j])
		{
		 v[0]=v[i];
		 v[i]=v[j];
		 v[j]=v[0];
		}
 for (i=1;i<=n;i++)
  for (j=i+1;j<=n-1;j++)
	{
	 x=j+1;
	 y=n;
	 while (x<=y)
	  {
	   m=(x+y)/2;
	   if (v[i]+v[j]<v[m])
		x=m+1;
	    else {
		  k++;
		  y=m-1;
		 }
	  }
	}
 printf("%d", k);

 return 0;
}