from math import gcd

def extgcd(a, b, x1=1, y1=0, x2=0, y2=1):
    if b == 0:
        return a, x1, y1
    q = a//b
    return extgcd(b, a%b, x2 ,y2, x1-x2*q, y1-y2*q)

def crt2(a, b, m1, m2):
    if a < b:
        a, b = b, a
        m1, m2 = m2, m1
    d, im1, im2 = extgcd(m1, m2)
    if a%d != b%d:
        return None
    mm = m1//d*m2
    x = (a - ((a-b)//d)*(m1*im1)) % mm
    return x, mm
def crt(as_, ms):
    x = as_[0]
    mm = ms[0]
    for a, m in zip(as_[1:], ms[1:]):
        t = crt2(a, x, m, mm)
        if t is None:
            return None
        x, mm = t
    return x, mm
n = int(input())
as_, ms = zip(*(map(int, input().split()) for _ in range(n)))

t = crt(as_, ms)
if t is None:
    print(-1)
else:
    x, mm = t
    if x == 0:
        x = mm
    print(x)