#include <map>

#include <cmath>

#include <queue>

#include <cstdio>

#include <cstring>

#include <iostream>

#include <algorithm>

using namespace std;

#define F(i,j,k) for (int i=j;i<=k;++i)

#define D(i,j,k) for (int i=j;i>=k;--i)

#define ll long long

#define mp make_pair

int n; ll ans; 

int main()

{

    scanf("%d",&n);

    printf("%.9lf\n",(double)(n/2.0/(2*n-1)*(n+1)));

}