#define _USE_MATH_DEFINES
#include<stdio.h>
#include<string>
#include<iostream>
#include<cctype>
#include<cstdio>
#include<vector>
#include<stack>
#include<queue>
#include <algorithm>
#include<math.h>
#include<set>
#include<map>
#include<iomanip>

//#include<bits/stdc++.h>



using namespace std;




int main() {

	int n;
	cin>>n;
	long long int x[100]={};
	x[1]=1,x[2]=1;
	for(int i=1;i<n;i++){
		x[i+1]+=x[i];
		x[i+2]+=x[i];
		
		//cout<<x[0]<<x[1]<<x[2]<<endl;

	}
	
	cout<<x[n]<<endl;
	
	return 0;
}