def ext_gcd(a, b): # ax + by = gcd(a, b)
    if b == 0:
        return (1, 0, a)
    x, y, g = ext_gcd(b, a % b)
    return (y, x - (a // b) * y, g)
def inv_gcd(a, b):
    x, y, g = ext_gcd(a, b)
    return (g, x % b)

# returns (x % lcm(M), lcm(M)),  (x = R[i] (mod M[i]))
def crt(R, M):
    N = len(R)
    r0 = 0
    m0 = 1
    for i in range(N):
        r1 = R[i] % M[i]
        m1 = M[i]
        if m0 < m1:
            r0, r1 = r1, r0
            m0, m1 = m1, m0
        if m0 % m1 == 0:
            if r0 % m1 != r1:
                return (0, 0) # x nai
            continue
        g, im = inv_gcd(m0, m1)
        u1 = m1 // g
        if (r1 - r0) % g != 0:
            return (0, 0) # x nai
        x = ((((r1 - r0) // g) % u1) * im) % u1
        r0 += x * m0
        m0 *= u1
        if r0 < 0:
            r0 += m0
    return (r0, m0)

N = int(input())
R = []
M = []
for i in range(N):
    x, y = map(int, input().split())
    R.append(x)
    M.append(y)
ans = crt(R, M)
if ans[1] == 0:
    print(-1)
else:
    if ans[0] == 0:
        print(ans[1] % (10 ** 9 + 7))
    else:
        print(ans[0] % (10 ** 9 + 7))