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.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication6
{

    class Program
    {
        static void Main(string[] args)
        {
            var Li = RL2IE().ToList();
            long ret = 0;
            var X = Li[0];
            var K = Li[1];
            var D = Li[2];
            var revert = K < 0;
            K = Math.Abs(K);
            if (K <= X / D)
            {
                ret =  X / D - K;
                ret *= D;
                
            }
            else
            {
                ret = X - D * (long)(X / D);
                if((K - (long)(X / D))%2!=0)ret-= D;
            }
            ret=Math.Abs(ret);
            Console.WriteLine(ret);
            Console.ReadLine();

        }

        static IEnumerable<long> RL2IE() { return spr(RL()).Select(x => (long)c2i(x)); }
        static string RL() { return Console.ReadLine().Trim(); }
        static IEnumerable<string> spr(string s) { return s.Split(' '); }
        static Int64 c2i(string c) { return Int64.Parse(c); }
        //static double c2d(string c) { return double.Parse(c); }
        static string bool2ret(bool b) { return b ? "Yes" : "No"; }
    }
}