#include <bits/stdc++.h>
using namespace std;
int main(){
	double i,o=1,p=1,u,sum=0;
	cin>>i;
	for(int k=0;k<i;k++)sum=sum+o/p,u=o+p,o=p,p=u;
	printf("%.3f",sum);
}
	
	

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