#include <iostream>
#include <cmath>
using namespace std;

//求第n个月兔子的总数量，a(n) = a(n-1) + a(n-2) 
int tuzi(int n){
	int r = 0;
	//交代起始项
	if(n == 1 || n == 2){
		r = 1;
	} else{
		r = tuzi(n - 1) + tuzi(n - 2); 	
	}
	
	return r;
}

int main(){
	int n,i;
	cin>>n;
	cout<<tuzi(n);
}

/**************************************************************
	Problem: 1238
	User: admin
	Language: C++
	Result: Accepted
	Time:18 ms
	Memory:2072 kb
****************************************************************/