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

namespace ABC175
{
    using static Ex;
    public class Solve
    {
        public static void Main(string[] args)
        {
            new ABC_C();
        }
    }
    public class ABC_A
    {
        public ABC_A()
        {
            var s = Read;
            int c = 0;
            int max = 0;
            for (int i = 0; i < 3; i++)
            {
                Maxs(ref max, c);
                if (s[i] == 'S') c = 0;
                else c++;
            }
            Maxs(ref max, c);
            max.Cw();
        }
    }
    public class ABC_B
    {
        public ABC_B()
        {
            int n = ReadInt;
            var l = ReadLongArray();
            //var set = new HashSet<long>(l);
            //n = set.Count;
            //l = set.ToArray();
            long cou = 0;
            for (int i = 0; i < n; i++)
            {

                for (int j = i + 1; j < n; j++)
                {

                    for (int k = j + 1; k < n; k++)
                    {
                        var a = l[i];
                        var b = l[j];
                        var c = l[k];
                        if (a != b && b != c && c != a
                            && (a + b > c)
                            && (c + b > a)
                            && (a + c > b))
                        {
                            //$"{i + 1} {j + 1} {k + 1}".Cw();
                            cou++;
                        }
                    }
                }
            }
            cou.Cw();
        }
    }
    public class ABC_C
    {
        public ABC_C()
        {
            var (x, k, d) = ReadLongArray().ToTpl3();
            x = Math.Abs(x);
            var div = x / d;
            var mod = x % d;
            if (k <= div)
            {
                (x - k * d).Cw();
                return;
            }
            k -= div;
            k %= 2;
            if (k == 0)
            {
                (mod).Cw();
                return;
            }
            (d - mod).Cw();
        }
    }

    public static class Ex
    {
        public static void Cw(this object s) { Console.WriteLine(s); }



        public static bool Mins<T>(ref T a, T b) where T : IComparable<T> { if (a.CompareTo(b) > 0) { a = b; return true; } return false; }
        public static bool Maxs<T>(ref T a, T b) where T : IComparable<T> { if (a.CompareTo(b) < 0) { a = b; return true; } return false; }
        public static void Swap<T>(ref T a, ref T b) { var t = b; b = a; a = t; }
        public static void Swap<T>(List<T> list, int i, int j) { T tmp = list[j]; list[j] = list[i]; list[i] = tmp; }

        public static long Lcm(int x, int y) { return x / Gcd(x, y) * y; }
        public static long Gcd(long m, long n) { if (n == 0) return m; return Gcd(n, m % n); }
        public static List<string> FastSort(this List<string> s) { s.Sort(StringComparer.Ordinal); return s.ToList(); }
        public static void yesno(this bool b) { (b ? "yes" : "no").Cw(); }
        public static void YesNo(this bool b) { (b ? "Yes" : "No").Cw(); }
        public static void YESNO(this bool b) { (b ? "YES" : "NO").Cw(); }

        public static string Read { get { return Console.ReadLine().Trim(); } }
        public static int ReadInt { get { return int.Parse(Read); } }
        public static long ReadLong { get { return long.Parse(Read); } }
        public static double ReadDouble { get { return double.Parse(Read); } }
        public static string[] ReadArray() { return Read.Split(' '); }
        public static int[] ReadIntArray() { return Read.Split(' ').Select(int.Parse).ToArray(); }
        public static long[] ReadLongArray() { return Read.Split(' ').Select(long.Parse).ToArray(); }
        public static string[] ReadArray(long N) { var v = new string[N]; for (long i = 0; i < N; ++i) v[i] = Read; return v; }
        public static int[] ReadIntArray(long N) { var v = new int[N]; for (long i = 0; i < N; ++i) v[i] = ReadInt; return v; }
        public static long[] ReadLongArray(long N) { var v = new long[N]; for (long i = 0; i < N; ++i) v[i] = ReadLong; return v; }

        public static (T, T) ToTpl2<T>(this T[] v) { return (v[0], v[1]); }
        public static (T, T, T) ToTpl3<T>(this T[] v) { return (v[0], v[1], v[2]); }
        public static (T, T, T, T) ToTpl4<T>(this T[] v) { return (v[0], v[1], v[2], v[3]); }
        public static (T, T, T, T, T) ToTpl5<T>(this T[] v) { return (v[0], v[1], v[2], v[3], v[4]); }
    }
}


Measured memory_bytes: 28240