from sys import stdin
readline = stdin.readline


def extended_gcd(x, y):
    if y == 0:
        return 1, 0, x
    a, b, c = extended_gcd(y, x % y)
    return b, a - x // y * b, c


def chinese(xy):
    xx, yy = 0, 1

    for x, y in xy:
        a, b, c = extended_gcd(yy, y)
        d, m = divmod(xx - x, c)
        if m:
            return -1
        yy = yy * y // c
        xx = (y * d * b + x) % yy
    return xx if xx else yy

n = int(readline())
xy = [list(map(int, readline().split())) for _ in range(n)]
ans = chinese(xy)
print(ans % 1000000007 if 0 < ans else -1)