CJam, 12 bytes
4 bytes saved thanks to Dennis!
lq'z,'a,-@erl_$q\@er
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Explanation
l e# read a line
_$ e# fancy way to obtain string "abc...z". Thanks to Dennis!
q e# read the rest of input as a string with newlines
'z,'a,- e# string "abc...z"
@ \@ e# swap, rotate
er e# transliterate. Implicit display
CJam, 12 bytes
lq'z,'a,-@er
Try it online!
Explanation
l e# read a line
q e# read the rest of input as a string with newlines
'z,'a,- e# string "abc...z"
@ e# rotate
er e# transliterate. Implicit display
CJam, 12 bytes
4 bytes saved thanks to Dennis!
l_$q\@er
Try it online!
Explanation
l e# read a line
_$ e# fancy way to obtain string "abc...z". Thanks to Dennis!
q e# read the rest of input as a string with newlines
\@ e# swap, rotate
er e# transliterate. Implicit display