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 Kotlin (1.3.71) (judge verdict: Accepted)

import kotlin.math.*

fun main() {
    println(solve())
}

val solve: () -> Any = {
    val (X, K, D) = readLongList()
    val n = X.absoluteValue / D
    (X.absoluteValue - when {
        n > K -> K * D
        (K - n) % 2 == 0L -> n * D
        else -> (n+1) * D
    }).absoluteValue
}

val mod: Int = 1_000_000_007


fun readString() = readLine()!!
fun readStringList() = readLine()!!.split(" ")
fun readInt() = readLine()!!.toInt()
fun readLong() = readLine()!!.toLong()
fun readIntList() = readLine()!!.split(" ").map(String::toInt)
fun readLongList() = readLine()!!.split(" ").map(String::toLong)

fun <T> T.alsoPrintln() = also { println(this) }

fun Boolean.toYesOrNo(yes: String = "Yes", no: String = "No") = if (this) yes else no

fun <E> List<E>.toPair() = this[0] to this[1]

fun <T> readPair(t: (String) -> T) = readPair(t, t)
fun <S, T> readPair(s: (String) -> S, t: (String) -> T) =
    readLine()!!.split(" ").let { Pair(s(it[0]), t(it[1])) }

fun Int.pow(n: Int) = this.toDouble().pow(n).toInt()

fun minAndMax(a: Int, b: Int) = if (a < b) a to b else b to a

fun <T> T.ifOrThis(bool: (T) -> Boolean, trans: (T) -> T) = if (bool(this)) trans(this) else this
fun <T> T.ifOrThis(bool: Boolean, trans: (T) -> T) = if (bool) trans(this) else this