#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: hulaoshi
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/