(declaim (optimize (speed 3) (safety 0) (debug 0)))

(defconstant +loop-count+ 1000000)
(defconstant +expected-checksum+ 5000001)

(declaim (ftype (function () fixnum) configured-loop-count))
(defun configured-loop-count ()
  (handler-case
      (let ((line (read-line *standard-input* nil nil)))
        (if line
            (let ((value (parse-integer line :junk-allowed t)))
              (if (> value 0) value +loop-count+))
            +loop-count+))
    (error () +loop-count+)))

(declaim (ftype (function (fixnum) fixnum) math-loop))
(defun math-loop (limit)
  (declare (type fixnum limit))
  (loop with i of-type fixnum = 0
        with acc of-type fixnum = 1
        while (< i limit)
        do (let* ((next (+ acc (* (+ i 3) 2)))
                  (bounded (if (> next 1000000000)
                               (- next 1000000000)
                               next)))
             (declare (type fixnum next bounded))
             (setf acc bounded
                   i (+ i 1)))
        finally (return acc)))

(let ((result (math-loop (configured-loop-count))))
  (format t "~D~%" result)
  (sb-ext:exit :code (if (= result +expected-checksum+) 0 1)))