#include<iostream>
#include<vector>
#include<algorithm>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<string>
#include<map>
#include<queue>

using namespace std;
 
template<typename T1, typename T2> istream& operator>>(istream& is, pair<T1,T2>& a){ return is >> a.first >> a.second; }
template<typename T1, typename T2> ostream& operator<<(ostream& os, pair<T1,T2>& a){ return os << a.first << " " << a.second; }
template<typename T> istream& operator>>(istream& is, vector< T >& vc){ for(int i = 0; i < vc.size(); i++) is >> vc[i]; return is; }
template<typename T> ostream& operator<<(ostream& os, vector< T >& vc){ for(int i = 0; i < vc.size(); i++) os << vc[i] << endl; return os; }
 
#define ForEach(it,c) for(__typeof (c).begin() it = (c).begin(); it != (c).end(); it++)
#define ALL(v) (v).begin(), (v).end()
#define UNQ(s) { sort(ALL(s)); (s).erase( unique( ALL(s)), (s).end());}

typedef pair< double , double > Pi;
typedef pair< double , Pi > Pii;
typedef long long int64;

int main(){
  int N;
  cin >> N;
  vector< int64 > 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;
}