(defun format-string (s) (let ((len (length s))) (loop for i below len do (format t "~c" (char s i)) (when (and (not (= i (1- len))) (zerop (mod (- len i 1) 3))) (format t ","))))) (defun main (&rest argv) (declare (ignorable argv)) (let ((s (read-line))) (format-string s) (terpri))) (main)