import math

def solve(n, m):
    g = math.gcd(n, m)
    n //= g
    m //= g

    d2, d5 = 0, 0
    while m % 2 == 0:
        m //= 2
        d2 += 1
    while m % 5 == 0:
        m //= 5
        d5 += 1

    if m > 1:
        return -1

    while n % 10 == 0:
        n //= 10

    while d2 < d5:
        n *= 2
        d2 += 1
    while d5 < d2:
        n *= 5
        d5 += 1

    return n % 10
    

def main():
    n = int(input())
    m = int(input())
    print(solve(n, m))
    
if __name__ == "__main__":
    main()