#include<fstream.h>

int n,x[801],nr;

void ordon()
{
	int i,j,aux;
	for(i=1;i<n;i++)
		for(j=i+1;j<=n;j++)
			if(x[i]>x[j]){aux=x[i];x[i]=x[j];x[j]=aux;}
}

int main()
{
	  ifstream f("nrtri.in");ofstream g("nrtri.out");
	  int i,j,k;
	  f>>n;for(i=1;i<=n;i++)f>>x[i];
	  ordon();
	  for(i=1;i<=n-2;i++)
		  for(j=i+1;j<=n-1;j++)
			  for(k=j+1;k<=n && x[i]+x[j]>=x[k];k++)nr++;
	  g<<nr;		  
	  f.close();g.close();
	  return 0;
}