#include<bits/stdc++.h>
using namespace std;
long long n,ans,s[100001];
int feibu(long long a)
{
	if(a==0||a==1)
		return 1;
	else
	{
		if(s[a-1]!=0&&s[a-2]!=0)
			return s[a-1]+s[a-2];
		else
		{
			s[a-1]=feibu(a-1);
			s[a-2]=feibu(a-2);
			return s[a-1]+s[a-2];
		}
	}
}
int main()
{
	cin>>n;
	ans=feibu(n);
	cout<<ans<<endl;
	return 0;
}