// No.1033 乱数サイ
package main

import "fmt"

func main() {
	var n, k float64
	fmt.Scan(&n, &k)

	exp := 0.0
	dm := (n + 1) * k //分母
	for i := 0.0; i <= n; i++ {
		exp += ((k * i) / dm)
	}
	fmt.Printf("%05f", exp)
}