using System;

public class Program

{

    private static string AddChecksum(string s)

    {

        int chksum = 0;

        foreach (char c in s)

        {

            chksum = chksum ^ c;

        }

        Console.WriteLine(chksum); // Print checksum decimal number

        s = "$" + s + "*" + chksum.ToString("X2") + ((char)13).ToString() + ((char)10).ToString();

        return s;

    }

    public static void Main()

    {

        string stcMsg = "SNSTC,-100,1";

        string rdrMsg = "SNRSA,-4, A,-4, A";

        Console.WriteLine(AddChecksum(rdrMsg)); // Print message with checksum

    }

}