(use gauche.array)

(let* ((n (string->number (read-line)))
       (weights (map string->number (string-split (read-line) #\space)))
       (total (fold + 0 weights))
       (max-weight 51)
       (arr (make-array (shape 0 (+ n 1) 0 (+ (* max-weight n) 1)) #f)))
  (array-set! arr 0 0 #t)

  (let loop ((weights weights)
	     (i 1))
    (cond ((null? weights)
	   (if (or (= (mod total 2) 1)
		   (eqv? (array-ref arr n (div total 2)) #f))
	       (print "impossible")
	       (print "possible")))
	  (else
	   (for-each
	    (lambda (j)
	      (let1 pred (- j (car weights))
		    (if (and (>= pred 0) (array-ref arr (- i 1) pred))
			(array-set! arr i j #t)))
	      (if (array-ref arr (- i 1) j)
		  (array-set! arr i j #t)))
	    (iota (+ (* max-weight n) 1)))
	   (loop (cdr weights) (+ i 1))))))