package main

import . "fmt"

var memo =map[int]float64{}

func f(n int) float64 {
	if n==0 {
		return 0
	}
	if n==1 {
		return 1
	}
	if z,ok:=memo[n]; ok{
		return z
	}
	var t float64
	for x:=0;x<=n-1;x++ {
		c1:=f(x)
		c2:=f(n-x-1)
		t+=(c1+c2+1)/float64(n)
	}
	memo[n]=t
	return t
}

func main() {
	var n int
	Scan(&n)
	Printf("%.10f\n", f(n))
}