#include<iostream>
#include<algorithm>

using namespace std;

#define NMAX 50

int main(){

	int N;
	long long dp[NMAX+1];

	for(int i=0;i<=NMAX;i++) dp[i]=0;
	dp[0]=1;

	for(int i=0;i<=NMAX;i++){
		if(i+1<=NMAX) dp[i+1]+=dp[i];
		if(i+2<=NMAX) dp[i+2]+=dp[i];
	}

	cin>>N;
	cout<<dp[N]<<endl;
}