#!/usr/bin/env crsn
(
    (:again)
    (ld r0 @cin
        (eof? (halt))
        (inval? (j :again)))
    (rcmp r0 'A' 'Z'
        (eq? (ld r1 'A'))
        (ne? (rcmp r0 'a' 'z'
            (eq? (ld r1 'a'))
            (ne? (j :print)))))
    (sub r0 r1)
    (add r0 13)
    (mod r0 26)
    (add r0 r1)
    (:print)
    (ld @cout r0)
    (j :again)
)