(defconstant +mod+ 1000000007)

(defun main (&rest argv)
  (declare (ignorable argv))
  (let* ((n (read))
         (res 0))
    (dotimes (_ n)
      (let* ((c (read))
             (d (read)))
        (incf res (mod (* (floor (1+ c) 2) d) +mod+))))
    (format t "~d~%" (mod res +mod+))))

(main)