#include <bits/stdc++.h>
using namespace std;
float ss(int n){
	float r;
	if(n==1||n==2){
		r=1.0;
	}
	else{
		r=ss(n-1)+ss(n-2);
	}
	return r;
}

int main(){
	int n,i;
	float s=0.0,k=1.0;
	cin>>n;
	for(i=2;i<=n+1;i++){
		s+=k/ss(i);
		k=ss(i);
	}
	printf("%.3f",s);
	return 0;
	}

/**************************************************************
	Problem: 1147
	User: fzy001
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/