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 Rust (1.42.0) (judge verdict: Accepted)

// -*- coding:utf-8-unix -*-

use proconio::input;

fn main() {
    input! {
        mut x: i64,
        mut k: i64,
        d: i64,
    }

    if x >= 0 {
        let simple_move_cnt = x / d;
        if simple_move_cnt >= k {
            println!("{}", x - k * d);
            return;
        }

        x -= simple_move_cnt * d;
        k -= simple_move_cnt;
        if k % 2 == 0 {
            println!("{}", x.abs());
        } else {
            println!("{}", (x - d).abs().min((x + d).abs()));
        }
    } else {
        let simple_move_cnt = -x / d;
        if simple_move_cnt >= k {
            println!("{}", (x + k * d).abs());
            return;
        }

        x += simple_move_cnt * d;
        k -= simple_move_cnt;
        if k % 2 == 0 {
            println!("{}", x.abs());
        } else {
            println!("{}", (x - d).abs().min((x + d).abs()));
        }
    }
}