def solve(n, m):
    x = m
    while x % 2 == 0:
        x //= 2
    while x % 5 == 0:
        x //= 5
    if x > 1:
        return -1

    r = 0
    while n > 0:
        while n < m:
            n *= 10
        r = n // m    
        n %= m
    while r % 10 == 0:
        r //= 10
    return r % 10


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