# -*- coding: UTF-8 -*-

def exgcd(a: int, b: int) -> (int, int, int):
    # 返回 (gcd(a,b), x, y) 满足 gcd(a,b)=ax+by
    x1, x2, x3, x4 = 1, 0, 0, 1
    while b != 0:
        q = a // b
        x1, x2, x3, x4, a, b = x3, x4, x1 - x3 * q, x2 - x4 * q, b, a - b * q
    return a, x1, x2


def gcrt2(a: int, m1: int, b: int, m2: int) -> (int, int):
    d, x, y = exgcd(m1, m2)
    bma = b - a
    if bma % d != 0:
        return -1, -1
    t, y = m2 // d, bma // d
    res = x * y % t
    if res < 0:
        res += t
    return res * m1 + a, m1 * t

if __name__ == '__main__':
    n = int(input())
    ans, m0 = 0, 1
    for _ in range(0, n):
        c, d = (int(i) for i in input().split(' '))
        ans, m0 = gcrt2(ans, m0, c, d)
        if ans == -1:
            break
    print(-1 if ans == -1 else ans % 1000000007)