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

/**************************************************************
	Problem: 1238
	User: fzy001
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/