public static class StringMath
{
    public static string Mult(string numA, string numB)
    {
        int memorize = 0;
        int c = 0;
        string zeros = "";
        string mult = "";
        string result = "0";
        for (int a = numA.Length - 1; a >= 0; a--)
        {
            for (int b = numB.Length - 1; b >= 0; b--)
            {
                c = int.Parse("" + numB[b]) * int.Parse("" + numA[a]) + memorize;
                if (a > 0 && b > 0) { memorize = c / 10; c = c % 10; }
                mult = "" + c + mult;
            }
            result = Add(result, mult + zeros);
            memorize = 0;
            zeros += "0";
            mult = "";
        }
        return result;
    }

    public static string Add(string numA, string numB)
    {
        string aN = "";
        string bN = "";
        string result = "";
        int c = 0;
        int memorize = 0;
        if (numA.Length > numB.Length) { aN = numA; bN = numB; }
        else { aN = numB; bN = numA; }
        for (int x = aN.Length - 1; x >= 0; x--)
        {
            if (x - (aN.Length - bN.Length) >= 0)
                c = int.Parse("" + aN[x]) + int.Parse("" + bN[x - (aN.Length - bN.Length)]) + memorize;
            else c = int.Parse("" + aN[x]) + memorize;
            if (x > 0) { memorize = c / 10; c = c % 10; }
            result = "" + c + result;
        }
        return result;
    }

    private static bool isBigger(string numA, string numB)
    {
        bool output = false;
        if (numA.Length > numB.Length) output = true;
        else if (numA.Length == numB.Length)
        {
            for (int x = 0; x < numA.Length; x++)
                if (int.Parse("" + numA[x]) > int.Parse("" + numB[x]))
                { output = true; x = numA.Length; }
                else if (int.Parse("" + numA[x]) < int.Parse("" + numB[x]))
                { output = false; x = numA.Length; }
                else output = false;
        }
        else output = false;
        return output;
    }

    private static bool isBiggerEqual(string numA, string numB)
    {
        if (numA == numB)
            return true;
        bool output = false;
        if (numA.Length > numB.Length) output = true;
        else if (numA.Length == numB.Length)
        {
            for (int x = 0; x < numA.Length; x++)
                if (int.Parse("" + numA[x]) > int.Parse("" + numB[x]))
                { output = true; x = numA.Length; }
                else if (int.Parse("" + numA[x]) < int.Parse("" + numB[x]))
                { output = false; x = numA.Length; }
                else output = false;
        }
        else output = false;
        return output;
    }

    private static bool isZero(string numA)
    {
        bool output = false;
        for (int i = 1; i < 10; i++)
            output = numA.Contains("" + i);
        return !output;
    }

    private static string clearZeros(string numA)
    {
        string output = "";
        char removeIt = '0';
        for (int i = 0; i < numA.Length; i++)
            if (numA[i] != removeIt) { output += numA[i]; removeIt = 'x'; }
        if (output.Length > 0)
            return output;
        else return "0";
    }

    public static string Sub(string numA, string numB)
    {
        string aN = "";
        string bN = "";
        string result = "";
        int zeros = 0;
        bool negative = false;
        int c = 0;
        int memorize = 0;
        if (numA.Length > numB.Length)
        { aN = numA; bN = numB; }
        else if (numA.Length == numB.Length)
        {
            for (int x = 0; x < numA.Length; x++)
                if (int.Parse("" + numA[x]) == int.Parse("" + numB[x]))
                {
                    aN = numA; bN = numB;
                    if (x == numA.Length - 1) return "0";
                    if (x < numA.Length - 1) zeros++;
                }
                else if (int.Parse("" + numA[x]) > int.Parse("" + numB[x]))
                {
                    if (x < numA.Length - 1) zeros++; aN = numA; bN = numB; x = numA.Length;
                }
                else if (int.Parse("" + numA[x]) < int.Parse("" + numB[x]))
                {
                    if (x < numA.Length - 1) zeros++;
                    aN = numB;
                    bN = numA;
                    negative = true;
                    x = numA.Length;
                }
        }
        else { aN = numB; bN = numA; negative = true; }
        for (int x = aN.Length - 1; x >= 0; x--)
        {
            if (x - (aN.Length - bN.Length) >= 0)
            {
                c = int.Parse("" + aN[x]) - int.Parse("" + bN[x - (aN.Length - bN.Length)]) + memorize;
                if (c < 0) { c += 10; memorize = -1; }
                else memorize = 0;
            }
            else
            {
                c = int.Parse("" + aN[x]) + memorize;
                if (c < 0) { c += 10; memorize = -1; }
                else memorize = 0;
            }
            if (result.Length <= aN.Length - zeros) { result = "" + c + result; }
        }
        if (!negative) return result; else return "-" + result;
    }

    public static string Dev(string numA, string numB)
    {
        if (isBigger(numB, numA)) return "0";
        else if (numA == numB) return "1";
        else if (numB == "1") return numA;
        else if (numB == "0") return "0";
        string result = "";
        string devide = numB;
        string smallerA = "";
        for (int x = 0; x < numA.Length; x++)
        {
            smallerA += numA[x];
            smallerA = clearZeros(smallerA);
            if (isBigger(smallerA, devide))
            {
                for (int i = 0; i < 11; i++)
                {
                    if (isBiggerEqual(smallerA, devide))
                    {
                        devide = Add(devide, numB);
                    }
                    else
                    {
                        devide = Sub(devide, numB);
                        smallerA = Sub(smallerA, devide);
                        result += "" + i % 10;
                        i = 12;
                        devide = numB;
                    }
                }
            }
            else if (smallerA == devide) { smallerA = "0"; result += "1"; devide = numB; }
            else
            {
                if (result.Length > 0) result += "0"; devide = numB;
            }
        }
        return result;
    }
}