#include<bits/stdc++.h>
using namespace std;
int main(){
	int m,n,i;
	double sum=0;
	cin>>n;
	int p=1,q=2;
	int pr=1,qr=2;
	i=2;
	sum=2;
	while(i<=n)
	{
		p=qr;
		q=pr+qr;
		pr=p;
		qr=q;
		sum=sum+1.0*q/p;
		i=i+1;
	}
	cout<<fixed<<setprecision(4)<<sum;
 	return 0;
}