I have received the following message that is encrypted with a Caesar cipher: JYMDWEFTQEBAF. This Caesar cipher replaces each letter of the plaintext (the message to be encrypted) with a letter that is a certain fixed number of positions along the 26-letter English alphabet. Knowing this fixed number of positions (the shift parameter) is the key to decrypt the message. For example, if the letter in the plaintext is A (the 1st letter of the alphabet) and the shift parameter is 4, then the encrypted letter is E (the 5th letter of the alphabet). Similarly, with a shift parameter of 7, Y (the 25th letter of the alphabet) is encrypted as F, which is the 32nd letter if the alphabet is repeated immediately after Z. I would like to decrypt the message that I have received but I do not know the shift parameter. I only know that the first letter of the plaintext is X.