#include <iostream>
using namespace std;
 
int main() {
   int n;
   cin >> n;
   int F[51] = {0, 1, 1, 2, 3};
   for(int i = 5; i <= n; i++) {
      F[i] = F[i-2] + F[i-3] + F[i-4];
   }
   cout << F[n];
   return 0;
}