#include <iostream>

using namespace std;


int F[45];

int main() {
  F[0] = 1;
  F[1] = 1;
  for (int i = 2; i < 45; ++i) {
    F[i] = F[i-1] + F[i-2];
  }

  int input;
  cin >> input;
  cout << F[input]<< endl;
}
  