from fractions import gcd


def sieve(n):
    s = [True] * n
    for x in range(2, int(n ** 0.5) + 1):
        if s[x]:
            for i in range(x + x, n, x):
                s[i] = False
    return [i for i in range(n) if s[i] and i > 1]


def solve():
    N = int(input())
    M = int(input())

    g = gcd(N, M)
    n = N // g
    m = M // g

    s = set()

    while True:
        while n < m:
            n *= 10
        x, n = divmod(n, m)
        if n in s:
            print(-1)
            return
        if n == 0:
            while x % 10 == 0:
                x //= 10
            print(x % 10)
            return
        s.add(n)

if __name__ == '__main__':
    solve()