import sys

sys.setrecursionlimit(10 ** 6)
import numpy as np

def II(): return int(sys.stdin.readline())

def main():
    def lowest(a):
        while a%10==0:a//=10
        a%=10
        print(a)
        exit()

    def cnt_factor(m):
        c2=c5=0
        while m&1==0:
            m>>=1
            c2+=1
        while m%5==0:
            m//=5
            c5+=1
        if m==1:return c2,c5
        return -1,-1

    n=II()
    m=II()
    g=np.gcd(m,n)
    n,m=n//g,m//g
    if m==1:lowest(n)
    c2,c5=cnt_factor(m)
    if c2==-1:print(-1)
    elif c2==c5:lowest(n)
    elif c2>c5:print(5)
    else:
        #/5=*0.2なのでc5回2をかけたときの最下位の数が答え
        c5-=c2
        n%=5
        print(pow(2,c5,10)*n%10)

main()