#include<iostream>
#include<iomanip>
using namespace std;


int digui(int n);

int main(){
	int n=0;
	double s=0;
	cin>>n;
	
	for(int i=1;i<=n;i++){
		s=s+digui(i)*1.0/digui(i+1);
		
	}
	
	cout<<setiosflags(ios::fixed)<<setprecision(3)<<s<<endl;
}

int digui(int n){
	if(n==1 || n==2){
		return 1;
	}
	else{
		return digui(n-1)+digui(n-2);
	}
}

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