#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;
	cin>>n;
	cout<<f(n);
}
/**************************************************************
	Problem: 1238
	User: linweilun
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/