#include <fstream>
#include <algorithm>

using namespace std;

ifstream fin("nrtri.in");
ofstream fout("nrtri.out");

int n,a[805],i,j,k,nr;
int main()
{
  fin>>n;
  for(i=1;i<=n;i++){fin>>a[i];}
  sort(a+1,a+n+1);
  for(i=1;i<=n-2;i++){for(j=i+1;j<=n-1;j++){k=j+1;
                                           while(a[i]+a[j]>=a[k]&&k<=n){nr++;
                                                                          k++;}
        }
  }
  fout<<nr;
    return 0;
}