(define (System.out.println x)
  (begin
    (display x)
    (newline)
  )
)

(let (
      (N (read))
     )
  (let loop(
            (i 0)
            (Sum 0)
           )
    (if (= i N)
        (System.out.println (modulo Sum 1000000007))
        (loop (+ i 1) (+ Sum (* (ceiling (/ (read) 2)) (read))))
    )
  )
)