#include<bits/stdc++.h>
#include<iostream>
using namespace std;
using LL = long long;
using P = pair<int,int>;
using Graph = vector<vector<int>>;
const long long LINF = 1LL << 60;
#define all(x) (x).begin(), (x).end()
#define rep(i,n) for(int i = 0; i < (n); ++i)
template<class T>void chmin(T&a, T b){if(a > b) a = b;}
template<class T>void chmax(T&a, T b){if(a < b) a = b;}

int main(){
  int N; cin >> N;
  vector<LL> dp(N+1, 0);
  dp[1] = 1;
  dp[2] = 2;
  for(int i = 3; i <= N; ++i){
    dp[i] = dp[i-1] + dp[i-2];
  }
  cout << dp[N] << endl;
}