#include<bits/stdc++.h>
using namespace std;
float ss(float n){
	float a;
	if(n<3){
		a=1;
	}else{
		a=ss(n-1)+ss(n-2);
	}
	return a;
}
int main()
{
	float i=1,s=0,n;
	cin>>n;
	while(i<=n){
		s+=ss(i)/ss(i+1);
		i++;
	}
	printf("%.3f",s);
	return 0;
}
/**************************************************************
	Problem: 1147
	User: zzz
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2076 kb
****************************************************************/