Mono-alphabetic substitution: Caesar

RootMe Challenge: Monoalphabetic substitution - Caesar: We just caught the messenger of the Emperor. He transmitted a coded message to his son. This could be an important message. You’ve to decrypt it ! To validate, you must enter the concatenation of the first letters of each line followed by the concatenation of the last letters of each line (for example : tfhqdlhfpkmeokgq).

I used Hack Caesar 26 and a pattern and poem emerged.