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 C# (.NET Core 3.1.201) (judge verdict: Wrong Answer)

using System;
using System.Linq;
using System.Collections.Generic;

namespace AtCoder0815
{
    class MainClass
    {
        public static void Main(string[] args)
        {
            //int N = int.Parse(Console.ReadLine());
            long[] XKD = Console.ReadLine().Split(' ').Select(x => long.Parse(x)).ToArray();
            long X = Math.Abs(XKD[0]);
            long K = XKD[1];
            long D = XKD[2];
            long ans = 0;
            long hikaku = 0;
            long hikaku2 = 0;

            if (K < X / D)
            {
                ans = X - K * D;
                if(ans == 0) { ans = D; }
            }

            if (K % 2 == 0 && K >= X / D)
            {
                ans = X - (X / D) * D;

                if (ans == 0)
                {
                    ans = D * (X / D);
                }
            }

            if (K % 2 == 1 && K >= X / D)
            {
                //ans = X - (D - (X - (X / D) * D));
                hikaku = X - (X / D) * D;
                hikaku2 = D - hikaku;
                ans = hikaku2;
                if(ans == 0)
                {
                    ans = 2 * D;
                }
            }

            Console.WriteLine(ans);
        }
    }
}