#include <iostream>
#include<algorithm>
#include<fstream>
using namespace std;
int v[805],n,i,j,k,nr;
int main()
{
    ifstream f("nrtri.in");
    ofstream g("nrtri.out");
    f>>n;
    for(i=1;i<=n;i++) f>>v[i];
    sort(v+1,v+n+1);
    for(i=1;i<=n-2;i++)
      for(j=i+1;j<=n-1;j++)
      {
          k=j+1;
          while(v[i]+v[j]>=v[k]&&k<=n) k++;
          nr=nr+k-1-j;
      }
      g<<nr;

    return 0;
}