#include <iostream>
using namespace std;
int num(int n);
int main()
{
  int n;
  cin >> n;
  cout << num(num(n)) <<endl;
  return 0;
}

int num(int n){
  if(n<0)return 0;
  if(n=0)return 1;
  return num(n-1)+num(n-2)+num(n-3);
}