from functools import *

def egcd(a, b):
    x, y, u, v = 0, 1, 1, 0
    while a != 0:
        q, r = b // a, b % a
        m, n = x - u * q, y - v * q
        b, a, x, y, u, v = a, r, u, v, m, n
    gcd = b
    return gcd, x, y

def lcm(a, b):
    from fractions import gcd
    return a // gcd(a, b) * b

def gcrt(congs):
    def fn(cong, prod):
        a, n = cong
        m = prod // n
        g, x, _ = egcd(m, n)
        return m // g * x * a

    def crt(a, b):
        N = a[1] * b[1]
        L = lcm(a[1], b[1])
        return (fn(a, N) + fn(b, N)) % L, L

    return reduce(crt, congs)

def main():
    N = int(raw_input())
    congs = [tuple([int(x) for x in raw_input().split(" ")]) for _ in range(N)]
    ans, mod = gcrt(congs)
    if ans == 0:
        ans = mod
    if any(ans % m != a for a, m in congs):
        print(-1)
    else:
        print(ans % (10**9 + 7))

if __name__ == "__main__":
    main()