// I SELL YOU...! 
#include<iostream>
#include<vector>
#include<algorithm>
#include<functional>
#include<queue>
#include<chrono>
#include<iomanip>
#include<map>
#include<set>
using namespace std;
using ll = long long;
using P = pair<ll,ll>;
using TP = tuple<ll,ll,ll>;
void init_io(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << setprecision(18);
}
signed main(){
  init_io();
  ll n;
  cin >> n;
  vector<ll> dp(n+1,0);
  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;
}