Need help with simple C# program

Type your programming task here… need comments within the program to explain the code etc and whats going on.

An Albanian social security number has a sequence of digits      

     followed by a letter. This ‘check’ letter is determined from      

     the values of the digits and is used to ensure that the numbers  

     are correct. Write a program that, when given a ten-digit        

     number and letter as input, calculates a unique ‘check’          

     character corresponding to the given number according to the      

     following rules:                                                  


     Add the five pairs of digits contained in the number              

     Take the remainder of dividing the result by 26                  

     Select the letter in that position of the alphabet, starting      

     with ‘A’ in position 0, ‘B’ in position 1, and so on.            


     For example, if the input is 1122334455J, the program should      

     calculate (11 + 22 + 33 + 44 + 55) % 26 giving 9, and so ‘J’      

     is the ‘check’ character. This means that the social security    

     number quoted is correct. If the input was 1122334455M, your      

     program should detect that the check letter is incorrect,        

     and therefore that this social security number is false.  

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