Caesar Cipher

Someone received a secret message. It is a string of uppercase Latin letters (ABCDEFGHIJKLMNOPQRSTUVWXYZ) that was encoded with a Caesar cipher. A Caesar cipher shifts every letter of the message forward by a fixed number of positions in the alphabet. Letters that run past the end of the alphabet wrap back around to its beginning. For example, encoding the message

ABCEGIKMOQSUVWXYZ

with a Caesar cipher of shift $4$ produces

EFGIKMOQSUWYZABCD

The recipient wants to decode the message but does not know which shift was used. Thanks to long linguistic experience, however, they do know which letter appeared most often in the original text. Moreover, that letter is unique: no two letters share the maximum number of occurrences in the original text.

Recover the original message.

The first line contains an integer $n$ ($1 \le n \le 10^6$), the length of the message, and an uppercase letter $c$, the letter that appears most frequently in the original message, separated by a single space. The second line contains the encoded message: exactly $n$ uppercase letters with no spaces.

Print the decoded original message on a single line. You may assume the original message can always be reconstructed uniquely.

In the example, the original text was cyclically shifted by $10$ positions along the alphabet. The letter that appears most often (four times) in the original message is A.