package main

import (
	"fmt"
)

func resolve(L, K int) int {
	ret := 0
	K2 := 2 * K
	for L > K2 {
		ret += K
		L -= K2
	}
	return ret
}

func main() {
	var L, K int
	fmt.Scanf("%d %d\n", &L, &K)
	fmt.Println(resolve(L, K))
}