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: Accepted)

using System.Linq;
using System.Text;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Diagnostics;
using System.Reflection.Metadata;
using System.Threading;
using System.Runtime.CompilerServices;
using System.IO.Pipes;

namespace AtCoder
{
    class Program
    {

        struct Point
        {
            public int x;
            public int y;

            public Point(int x, int y)
            {

                this.x = x;
                this.y = y;

            }

        }


        const int BiggestMod = 1000000007;

        public static void Main()
        {

            var args = Console.ReadLine().Split(' ').Select(x => long.Parse(x)).ToArray();
            var x = Math.Abs(args[0]);
            var k = args[1];
            var d = args[2];
            var ans = 0L;

            var min = x / d;

            if (min >= k)
                ans = x - (k * d);
            else
            {

                var buf = k - min;
                if ((buf & 1) == 0)
                    ans = x - min * d;
                else
                    ans = Math.Abs(x - (min + 1) * d);

            }

            Console.WriteLine(ans);

        }

    }

}