package main

import . "fmt"
import . "sort"

func main() {
	var a,b int
	Scan(&a,&b)
	c:=Search(a,func(i int)bool{
	 x:=int64(i)*int64(b)
	 y:=int64(a)
	 return y-x-x<=int64(b)
	 
	})
	Println(c*b)
}