Problem:
Score : 300 points

Problem Statement

Takahashi, who lives on the number line, is now at coordinate X. He will make exactly K moves of distance D in the positive or negative direction.

More specifically, in one move, he can go from coordinate x to x + D or x - D.

He wants to make K moves so that the absolute value of the coordinate of the destination will be the smallest possible.

Find the minimum possible absolute value of the coordinate of the destination.

Constraints

-10^{15} \leq X \leq 10^{15}

1 \leq K \leq 10^{15}

1 \leq D \leq 10^{15}

All values in input are integers.

Input

Input is given from Standard Input in the following format:

X K D

Output

Print the minimum possible absolute value of the coordinate of the destination.

Sample Input 1

6 2 4

Sample Output 1

2

Takahashi is now at coordinate 6. It is optimal to make the following moves:

Move from coordinate 6 to (6 - 4 =) 2.

Move from coordinate 2 to (2 - 4 =) -2.

Here, the absolute value of the coordinate of the destination is 2, and we cannot make it smaller.

Sample Input 2

7 4 3

Sample Output 2

1

Takahashi is now at coordinate 7. It is optimal to make, for example, the following moves:

Move from coordinate 7 to 4.

Move from coordinate 4 to 7.

Move from coordinate 7 to 4.

Move from coordinate 4 to 1.

Here, the absolute value of the coordinate of the destination is 1, and we cannot make it smaller.

Sample Input 3

10 1 2

Sample Output 3

8

Sample Input 4

1000000000000000 1000000000000000 1000000000000000

Sample Output 4

1000000000000000

The answer can be enormous.

Solution in Go (1.14.1) (judge verdict: Wrong Answer)

package main

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

var sc = bufio.NewScanner(os.Stdin)

func nextInt() int {
	sc.Scan()
	i, e := strconv.Atoi(sc.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func nextFloat64() float64 {
	sc.Scan()
	i, e := strconv.ParseFloat(sc.Text(), 64)
	if e != nil {
		panic(e)
	}
	return i
}

func nextString() string {
	sc.Scan()
	return sc.Text()
}

func abs(x int) int {
	if x < 0 {
		return -1 * x
	} else {
		return x
	}
}

func main() {
	sc.Split(bufio.ScanWords)
	//sc.Buffer(nil, 100000000)

	x, k, d := nextInt(), nextInt(), nextInt()

	dt := x / d

	if dt > k {
		if x > 0 {
			fmt.Println(abs(x - (k * d)))
		} else {
			fmt.Println(abs(x + (k * d)))
		}
		return
	}

	var rest int
	if x > 0 {
		rest = x - (dt * d)
	} else {
		rest = x + (dt * d)
	}
	restK := k - dt

	if restK%2 == 0 {
		fmt.Println(abs(rest))
	} else {
		if rest > 0 {
			fmt.Println(abs(rest - d))
		} else {
			fmt.Println(abs(rest + d))
		}
	}
}