(defun sieve (limit) (let ((is-prime (make-array (1+ limit) :initial-element t))) (setf (aref is-prime 0) nil (aref is-prime 1) nil) (loop for i from 2 to (isqrt limit) do (when (aref is-prime i) (loop for j from (* i i) to limit by i do (setf (aref is-prime j) nil)))) (loop for i from 2 to limit when (aref is-prime i) collect i))) (defun prime-factors (n primes) (let ((factors '())) (dolist (prime primes) (loop while (zerop (mod n prime)) do (push prime factors) (setf n (/ n prime)))) (if (> n 1) (push n factors)) (nreverse factors))) (defun first-factor-pair (n) (if (<= n 1) (list 1 1) (let* ((limit (isqrt n)) (primes (sieve limit)) (factors (prime-factors n primes))) (list 1 (apply #'* factors))))) (defun main () (let ((n (parse-integer (read-line)))) (let ((pair (first-factor-pair n))) (format t "~{~a~^ ~}~%" pair)))) (main)