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

}

/**************************************************************
	Problem: 1238
	User: houshanglin
	Language: C++
	Result: Accepted
	Time:13 ms
	Memory:2072 kb
****************************************************************/