(define (extended-euclidean-algorithm a b)
  (if (= b 0)
    (list a 1 0)
    (let*
      (
        (result (extended-euclidean-algorithm b (modulo a b)))
        (g (car result))
        (x (cadr result))
        (y (caddr result))
      )
      (list g y (- x (* y (quotient a b)))))))

(define (chinese-remainder-theorem rs ms)
  (let loop ((r (car rs)) (m (car ms)) (rx (cdr rs)) (mx (cdr ms)))
    (if (or (null? rx) (null? mx))
      (cons r m)
      (let*
        ((r0 (car rx)) (m0 (car mx)))
        (if (and (= r0 -1) (= m0 0))
          (cons -1 0)
          (let*
            (
              (r1 (modulo r0 m0))
              (g (gcd m m0))
              (l (lcm m m0))
            )
            (if (not (= (modulo r g) (modulo r1 g)))
              (cons -1 0)
              (let*
                (
                  (euclid-result (extended-euclidean-algorithm (/ m0 g) (/ m g)))
                  (x (cadr euclid-result))
                )
                (loop
                  (modulo (+ r1 (* m0 (* (/ (- r r1) g) (modulo x (/ m g))))) l)
                  l
                  (cdr rx)
                  (cdr mx))))))))))

(define yuki187
  (let
    ((r '()) (m '()))
    (do
      ((i (string->number (read-line)) (- i 1)))
      ((zero? i))
      (let*
        (
          (vals (map string->number (string-split (read-line) #\space)))
          (a (car vals))
          (b (cadr vals))
        )
        (set! r (cons a r))
        (set! m (cons b m))
      )
    )
    (let*
      (
        (rm (chinese-remainder-theorem r m))
        (k (car rm))
        (s (cdr rm))
        (MOD 1000000007)
      )
      (display
        (cond
          ((= k -1) -1)
          ((zero? k) (modulo s MOD))
          (else (modulo k MOD))
        )
      )
    )
  )
)