#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

long long dp[55];

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