using System;

​

public class Program

{

    public static void Main()

    {

        var safd = getSum("$GNRMC,130500.00,A,5919.50601,N,01805.07715,E,12.359,86.70,170122,6.75,E,D*");

        var safd2 = getSum("GNRMC,130501.00,A,5919.50631,N,01805.08392,E,12.349,83.78,170122,6.75,E,D*");

        Console.WriteLine(safd);

        Console.WriteLine(safd2);

    }

​

   public static string getSum(String str) 

   {

    int checksum = 0;

    if (str.StartsWith("$")) {

        str = str.Substring(1, str.Length - 1);

    }

​

    int end = str.IndexOf('*');

    if (end == -1)

        end = str.Length;

    for (int i = 0; i < end; i++) {

        checksum = checksum ^ str[i];

    }

    string hex = checksum.ToString("X");

    if (hex.Length == 1)

        hex = "0" + hex;

    return hex.ToUpper();

    }

}