#include<bits/stdc++.h>
using namespace std;
int main()
{
	int n;
	cin>>n;
	long long a[60];
	a[1]=1;
	a[2]=1;
	for(int i=3;i<=n;i++)
	{
		a[i]=a[i-2]+a[i-1];
	}
	cout<<a[n];
	return 0;
}
/**************************************************************
	Problem: 1238
	User: chenkexin
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:2072 kb
****************************************************************/