#include<fstream>
#include<algorithm>
using namespace std;

int a[802],n,i,j,k,nr;
int main()
{
	ifstream f("nrtri.in");
	ofstream g("nrtri.out");
  f>>n;
   for(i=1;i<=n;i++)
		f>>a[i];
   sort(a,a+n+1);
   for(i=1;i<n-1;i++)
	   for(j=i+1,k=i+2;j<n;j++)
	   {
		   while(k<=n&&a[j]+a[i]>=a[k])
			   k++;
		   nr+=k-j-1;
	   }
   g<<nr;
   return 0;
}