#include <bits/stdc++.h>
using namespace std;
int N;
vector<long long> memo(60);

int main() {
  cin >> N;
  memo[1]=1;
  memo[2]=2;
  for(int i=3;i<=50;i++){memo[i]=memo[i-1]+memo[i-2];}
  cout << memo[N] << endl;
}