#include<bits/stdc++.h>
using namespace std;
int f(int n){
	int r=0;
	if(n==1||n==2) r=1; 
	else r=f(n-1)+f(n-2);
	return r;
}
int main(){
	int n,h=0;
	cin>>n;
	cout<<f(n);
	return 0;
}
/**************************************************************
	Problem: 1238
	User: hongjiaming
	Language: C++
	Result: Accepted
	Time:14 ms
	Memory:2072 kb
****************************************************************/