import sys

sys.setrecursionlimit(10 ** 6)
def II(): return int(sys.stdin.readline())
def MI(): return map(int, sys.stdin.readline().split())

def gcd(a, b):
    while b: a, b = b, a % b
    return a

def lcm(a, b):
    return a * b // gcd(a, b)

def extgcd(a, b, c):
    if b == 0: return c // a, 0, abs(a)
    x, y, g = extgcd(b, a % b, c)
    return y, x - y * (a // b), g

def main():
    n = II()
    x1, y1 = MI()
    for _ in range(n - 1):
        x2, y2 = MI()
        p, q, g = extgcd(y1, -y2, x2 - x1)
        if (x2 - x1) % g > 0:
            print(-1)
            exit()
        x1 = y1 * p + x1
        y1 = lcm(y1, y2)
    ans = (x1 - 1) % y1 + 1
    print(ans)

main()