using System;

public class Program

{

    public static void Main()

    {

            var secret = SimpCryptDec("8610ecd39e8fcd9c95ecfecd9e");

            Console.WriteLine(secret);

    }

// Define other methods and classes here

public static int HexDigit(char digit)

{

    if ((digit >= '0') && (digit <= '9'))

        return digit - '0';

    if ((digit >= 'a') && (digit <= 'f'))

        return digit - 'a' + 10;

    if ((digit >= 'A') && (digit <= 'F'))

        return digit - 'A' + 10;

    return -1;

}

​

public static int Hex2C(char digit1, char digit2)

{

    int i1, i2;

​

    i1 = HexDigit(digit1);

    i2 = HexDigit(digit2);

    if ((i1 == -1) || (i2 == -1))

        return 0;

    return (i1 << 4) | i2;

}

​

public static string SimpCryptDec(string input)

{

    string result = string.Empty;

    string p2;

    int old = 0;

    int newValue= 0;

    int nc2 = 0;

    int cv = 0;

    bool skip = true;

    if (string.IsNullOrEmpty(input) || ((input.Length < 2) || (input.Length > 400)))

    {

        return result;

    }

    p2 = input;

    for (int i = 0; i < input.Length; i+=2)

    {

        newValue= Hex2C(input[i],input[i+1]);

        newValue = newValue ^ old ^ nc2 ^ cv;

        cv++;

        if (skip)

        {

            skip = false;

            if ((newValue & 2) == 0)

            {

                nc2 = newValue ^ 0xa9;

            }

            else

            {

                nc2 = newValue ^ 0x5c;

            }

        }

        else

        {

            result += (char)newValue;

        }

        old = newValue;

    }

    return result;

}

}

​

​