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

/**************************************************************
	Problem: 1147
	User: zhuanghaoxiang
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/