#include<iostream>
using namespace std;
#include<cstring>
#include<stdio.h>
double a[100005];
int main()
{
int i,j,k;
int N;
a[0]=0;
a[1]=1;
a[2]=3.0;
for(i=3;i<100001;i++)
k=(1+i)/2;
a[i]=a[k-1]+k-1+a[i-k]+i-k+1;
}
while(cin>>N)
printf("%.2lf\n",a[N]/N);
return 0;