(defun r (x y)
  (sqrt (+ (expt x 2) (expt y 2))))

(defun f628 (n)
  (print (elt (sort (loop for x from 1 to n
						  nconc (loop for y upto x collect (r x y)))
					#'<)
			  (1- n))))

(f628 1)
(f628 2)
(f628 5)
(f628 9)