#define _USE_MATH_DEFINES
#include<iostream>
#include<vector>
#include<algorithm>
#include<cmath>
#include<string>
#include<iomanip>
#include<numeric>
#include<queue>
#include<deque>
#include<stack>
#include<set>
#include<map>
#include<random>
#include<bitset>
#include<cassert>
#include<complex>
#include<fstream>
#include<cstdlib>
#include<functional>
#include<array>
using namespace std;
typedef long long ll;
const int mod=998244353;
const int dx[]={1,0,0,-1},dy[]={0,1,-1,0};
ll dp[51];
int main(){
	int n;
	cin>>n;
	dp[0]=1;
	for(int i=1;i<=n;i++){
		dp[i]+=dp[i-1];
		if(i>=2)
			dp[i]+=dp[i-2];
	}
	cout<<dp[n]<<endl;
}