import sys
import math

input = sys.stdin.readline


def main():
    N = int(input())
    M = int(input())
    M *= 10**50
    for i in range(200):
        g = math.gcd(N, M)
        N //= g
        M //= g
        if M == 1:
            print(N % 10)
            return
        N *= 10

    print(-1)


if __name__ == '__main__':
    main()