A Caesar $($or rotation$)$ cipher is a simple system of encoding strings by shifting every letter forward $($or backward$)$ by a given amount. For example, if the shift amount is $3,$ then the letter A becomes D$,$ B becomes E$,$ C becomes F$,$ and so on$.$ Letters near the end of the alphabet wrap around; for a shift of $3,$ X becomes A$,$ Y becomes B$,$ Z becomes C$.$