#include<bits/stdc++.h>
using namespace std;
int f(int m){
	int r=0;
	if(m==2||m==2) r=1;
	else r=f(m-1)+f(m-2);
	return r;
} 
int main(){
	int n,s=0;
	cin>>n;
	
	cout<<f(n);
}
/**************************************************************
	Problem: 1238
	User: huxuanchen
	Language: C++
	Result: Memory Limit Exceed
****************************************************************/