#include<bits/stdc++.h>
using namespace std;
int main(){
	double n,sum=1,a=0;
	cin>>n;
	for(double i=2;i<=n;i+=2){
		sum=sum-(1.0/i)+(1.0/(i+1.0));
	}
	printf("%.4lf",sum);
	return 0;
}