#include<bits/stdc++.h>
using namespace std;
int main(){
	int i=1;
	double s=0,n,c=0;
	cin>>n;
	while(i<=n){
		if(i%2!=0){
			s=1*1.0/i+s;	
		}
		else{
			c=1*1.0*(-1)/i+c;
		}
		i++;
	}
	cout<<fixed<<setprecision(4)<<s+c;
	return 0;
}