#include <bits/stdc++.h>
using namespace std;
unsigned n;
unsigned A(unsigned x){
	if(x==1){
		return 1;
	}else if(x==2){
		return 2;
	}
	return A(x-1)+A(x-2);
}
int main (){
	cin>>n;
	cout<<A(n);
	return 0;
}