from fractions import gcd

def inv(a, m):
    b, x, y = m, 1, 0
    while b != 0:
        t = a // b
        a, b = b, a - t * b
        x, y = y, x - t * y
        pass
    return x % m

def CRT(congs):
    x, m = 0, 1
    for y, n in congs:
        g = gcd(m, n)
        if x % g != y % g: return -1, -1
        m //= g; n *= m; m *= gcd(m, g); n //= m
        x %= m; x += (y - x % n + n) * inv(m, n) % n * m; m *= n
        pass
    return x, m

mod = 10 ** 9 + 7

n = input()
congs = [map(int, raw_input().split()) for _ in xrange(n)]

ans = CRT(congs)[0]
print -1 if ans == -1 else ans % mod