#include <fstream>
using namespace std;
ifstream f ("nrtri.in");
ofstream g ("nrtri.out");
int i,j,k,v[801],aux,contor=0,n;
int main ()
   { for (i=1;i<=n;i++)
    f>>n;
     for (i=1;i<=n;i++)
      for (j=i+1;j<=n;j++)
       { aux=v[i];
        v[i]=v[j];
        v[j]=aux;}
        for (i=1;i<=n;i++)
        for (j=i+1;j<=n;j++)
        for (k=j+1;k<=n;k++)
        if (v[i]+v[j]>=v[k])
        contor++;
        g<<contor;
        g.close();
        system ("pause");
        return 0 ;
}