package main

import (
	"bufio"
	"fmt"
	"io"
	"os"
	"strconv"
)

func main() {
	sc := NewScanner(os.Stdin)
	L, _ := sc.NextInt()
	K, _ := sc.NextInt()

	fmt.Println(solve(L, K))
}

func solve(l, k int) int {
	n := 0
	if l%(2*k) == 0 {
		n--
	}
	return (n + l/(2*k)) * k
}

type scanner struct {
	*bufio.Scanner
}

func NewScanner(r io.Reader) *scanner {
	return &scanner{
		bufio.NewScanner(r),
	}
}

func (s *scanner) Next() (string, error) {
	s.Scanner.Split(bufio.ScanWords)
	return s.nextToken()
}

func (s *scanner) nextToken() (string, error) {
	sc := s.Scanner
	if sc.Scan() {
		return sc.Text(), nil
	}
	if sc.Err() != nil {
		return "", sc.Err()
	}
	return "", io.EOF
}

func (s *scanner) NextInt() (int, error) {
	token, err := s.Next()
	if err != nil {
		return 0, err
	}
	return strconv.Atoi(token)
}