(define (iota n . args)
  (let ((start (if (pair? args) (car args) 0))
        (step  (if (and (pair? args) (pair? (cdr args))) (cadr args) 1)))
    (let loop ((m n) (last (+ start (* step (- n 1)))) (a '()))
      (if (zero? m)
          a
	  (loop (- m 1) (- last step) (cons last a))))))

(define (solve CD)
  (if (null? CD)
      0
      (let ((C (car (car CD))) (D (cdr (car CD))))
	(remainder (+ (* D (quotient (+ C 1) 2)) (solve (cdr CD))) 1000000007))))

(display (solve (let ((N (read))) (map (lambda (x) (cons (read) (read))) (iota N)))))
(newline)