Problem 19

(defun check (m y)
  (equal 6 (nth 6 (multiple-value-list
                    (decode-universal-time
                      (encode-universal-time 0 0 0 1 m y))))))
(print (loop for i from 1 to 100 sum
             (loop for j from 1 to 12 sum
                   (if (check j (+ 1900 i)) 1 0))))