#include<fstream>
using namespace std;
int n,i,j,nr,aux,a[30001];
int main()
{
    ifstream f("heta.in");
    ofstream g("heta.out");
    f>>n;
    for(i=1;i<=n;i++)
    f>>a[i];
    for(i=1;i<=n-2;++i)
      for(j=i+1;j<=n-1;++j)
         {
            int k=j+1;
            while(a[i]+a[j]>=a[k] && k<=n)
               ++k;
            nr=nr+k-j-1;

         }
         g<<nr;
    return 0;
}