def read_data():
    N = int(input())
    xy = []
    for n in range(N):
        x, y = map(int, input().split())
        xy.append((x, y))
    return N, xy


def gcd_ext(m, n):
    x, y, u, v = 1, 0, 0, 1
    while n:
        k, m = divmod(m, n)
        m, n = n, m
        x, y, u, v = u, v, x - u * k, y - v * k
    return m, x, y


def solve2(x1, y1, x2, y2):
    gcd, a, b = gcd_ext(y1, y2)
    lcm = y1 * y2 // gcd
    k, r = divmod(x1 - x2, gcd)
    if r != 0:
        return -1, lcm
    z = (x1 - k * a * y1) % lcm
    return z, lcm


def solve(N, xy):
    x0, y0 = xy[0]
    if N == 1:
        return x0 if x0 else y0
    mod = 10 ** 9 + 7
    for x1, y1 in xy[1:]:
        x0, y0 = solve2(x0, y0, x1, y1)
        if x0 == -1:
            return -1
        x0 %= mod
    return x0 if x0 else y0

N, xy = read_data()
print(solve(N, xy))