#include <iostream>
using namespace std;

int main(){
  
  int n;
  long long dp[55] = {0};
  cin >> n;
  
  dp[0] = dp[1] = 1;
  for(int i = 2; i <= n; i++){
    dp[i] = dp[i - 1] + dp[i - 2];
  }
  
  cout << dp[n] << endl;
}