def modulo(x, y):
    return (x % y + y) % y


def floor(x, y):
    r = modulo(x, y)
    return (x - r) // y


def gcd(a, b):
    if b == 0:
        return a
    else:
        return gcd(b, modulo(a, b))


def ext_gcd(a, b):
    if b == 0:
        return a, 1, 0
    else:
        g, x, y = ext_gcd(b, modulo(a, b))
        return g, y, x - floor(a, b) * y


def crt(ss):
    r = 0
    m = 1
    for bi, mi in ss:
        g, p, _ = ext_gcd(m, mi)
        if (bi - r) % g != 0:
            return -1, -1
        t = modulo(floor(bi - r, g) * p, floor(mi, g))
        r = r + m * t
        m = floor(m * mi, g)
        r = modulo(r, m)
    return r, m


def main():
    n = int(input())
    rs = []
    for _ in range(n):
        rs.append(list(map(int, input().split())))
    ans, _ = crt(rs)
    print(ans)


if __name__ == "__main__":
    main()