#include <fstream>
#include <algorithm>

using namespace std;

int sol, n, i, j, k, a[801];

int main () {
  ifstream fi("nrtri.in");
  ofstream fo("nrtri.out");
  fi >> n;
  for (i = 1; i <= n; i++)
    fi >> 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 (k <= n and a[k] <= a[i]+a[j])
        k++;
      sol += k-j-1;
    }
  fo << sol;
  return 0;
}