#include <iostream>
using namespace std;

int S[50];

int main()
{
  int n;
  S[0] = S[1] = 1;
  for (int i = 2; i < 45; i++){
    S[i] = S[i - 1] + S[i - 2];
  }
  cin >> n;
  cout << S[n] << endl;
}