The following ciphertext has been derived from a simple substitution cipher of the form Ci = Pi + N. Find the value of N that decrypts the ciphertext, decrypt it, and write the plaintext below. The numbers and letters below the ciphertext are there to make your task easier. You do not need to write down the value of N in your answer. Enter your answer using only upper case letters.

IGT EUA YKK ZNK SUUT GZ TUUT OT PATK?

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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