#include<bits/stdc++.h>
using namespace std;
int d(int o){
	int r;
	if(o==2||o==1){
		r=1;
	}
	else{
		r=d(o-1)+d(o-2); 
	}
	return r; 
}
int main()
{
	int n;
	float s=0;
	cin>>n; 
	for(int i=1;i<=n;i++){
		s=s+(d(i)*1.0/d(i+1));
	} 
	printf("%.3f",s);
	return 0;
}

/**************************************************************
	Problem: 1147
	User: houshanglin
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2076 kb
****************************************************************/