#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	double s=0.0,r=1,d=1,t;
	cin>>n;
	for(int i=1;i<=n;i++){
		s+=r/d;
		t=r;
		r=d;
		d=t+d;
	}
	printf("%.3f",s);
}

/**************************************************************
	Problem: 1147
	User: wangyiyang
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/