(let(
     (foo (read (current-input-port)))
     )
    (let loop((i 0))
         (begin
         (if (char-upper-case? (string-ref foo i))
                 (string-set! foo i (char-downcase (string-ref foo i)))
                 (string-set! foo i (char-upcase   (string-ref foo i))))
        (if (<= i (- (string-length foo) 1))
            (loop (+ i 1))
            (begin (display foo) (newline))
        )
)
  )
  )