#include <iostream>
#include <fstream>
#include <algorithm>

using namespace std;

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

const int L=9;
int v[801], n;

int binary_search(int x)
{
  int pas=1 << L, r=0, rez=0, i, j;
  
  while(pas)
  {
    if(r+pas<=n && v[r+pas]<=x) r+=pas;
          
          pas/=2;
  }
  return r;
}

int main()
{
  fin>>n;
  int i, j, sum=0, rez=0, c;
  for(i=1; i<=n; i++)
       fin>>v[i];
  
  sort(v+1, v+n+1);
  
  for(i=1; i<=n; i++)
  {
    for(j=i+1; j<=n; j++)
    {
      sum=v[i]+v[j];
      rez+=binary_search(sum)-j;
    }
  }
  fout<<abs(rez);
    return 0;
}