import math

def main():
    N = int(input())
    M = int(input())
    g = math.gcd(N, M)
    N //= g
    M //= g
    m = M

    while m % 5 == 0:
        m //= 5
    while m % 2 == 0:
        m //= 2

    if m != 1:
        print(-1)
    else:
        while N % M != 0:
            N *= 10
        res = N // M
        while res % 10 == 0:
            res //= 10

        print(res % 10)
    
if __name__ == '__main__':
    main()