package main import ( "bufio" "fmt" "math" "os" "strconv" ) const MaxInt = math.MaxInt64 var scanner *bufio.Scanner func main() { l, k := Int(), Int() fmt.Println(((l - 1) / (2 * k)) * k) } func init() { scanner = bufio.NewScanner(os.Stdin) scanner.Buffer([]byte{}, MaxInt) scanner.Split(bufio.ScanWords) } func Int() int { scanner.Scan() ret, _ := strconv.ParseInt(scanner.Text(), 10, 0) return int(ret) } func Ints(n int) []int { ret := make([]int, n) for i := 0; i < n; i++ { ret[i] = Int() } return ret } func Max(a, b int) int { if a < b { return b } return a } func Min(a, b int) int { if a < b { return a } return b }