#include<iostream>
#include<string>
#include<iomanip>
#include<cmath>
#include<vector>
#include<algorithm>

using namespace std;

#define int long long
#define rep(i,n) for(int i = 0; i < (n); i++)
#define INF ((long long)1e18)
#define EPS (1e-5)
#define MOD ((int)1e9+7)
#define endl "\n"

#define yn(f) ((f)?"Yes":"No")
#define YN(f) ((f)?"YES":"NO")

signed main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	cout<<fixed<<setprecision(10);
	
	int N;
	int dp[2][100] = {};
	
	cin>>N;
	
	dp[0][0] = 1;
	
	for(int i = 0; i < N; i++){
		// dp[0][i+1] += dp[1][i];
		// dp[0][i+1] += dp[0][i];
		// dp[1][i+2] += dp[0][i];
		dp[0][i+1] += dp[0][i];
		dp[0][i+2] += dp[0][i];
	}
	
	cout<<dp[0][N]<<endl;
	
	return 0;
}