def exgcd(a,b,x,y):
    if not b:
        x,y = 1,0
        return a,x,y

    d,x,y = exgcd(b, a % b, y, x)
    temp = y
    y = x - a // b * y
    x = temp
    return d,x,y

if __name__ == "__main__":
    n = int(input())
    a1,m1 = map(int,input().split())

    for i in range(n-1):
        a2,m2 = map(int,input().split())

        k1,k2 = 0, 0

        d,k1,k2 = exgcd(a1,a2,k1,k2)

        if (m2-m1) % d:
            print(-1)
            exit()

        k1 *= (m2-m1) // d
        t = a2 // d
        k1 = k1 % t
        m1 = a1 * k1 + m1
        a1 = abs(a1 // d * a2)

    print(m1 % a1)