#include <iostream>
using namespace std;
 
int main() {
   int n;
   cin >> n;
   long long arr[61];
   arr[0] = 1;
   arr[1] = 1;
   arr[2] = 2;
   for(int i = 3; i <= n; i++){
      arr[i] = arr[i-1] + arr[i-2] + arr[i-3];
   }
   cout << arr[n];
   return 0;
}