import sys
from math import gcd
sys.setrecursionlimit(10**7)
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int,sys.stdin.readline().rstrip().split())
def LI(): return list(map(int,sys.stdin.readline().rstrip().split()))
def LI2(): return list(map(int,sys.stdin.readline().rstrip()))
def S(): return sys.stdin.readline().rstrip()
def LS(): return list(sys.stdin.readline().rstrip().split())
def LS2(): return list(sys.stdin.readline().rstrip())


N,M = I(),I()
g = gcd(N,M)
N //= g
M //= g

X = M
a,b = 0,0
while X % 2 == 0:
    X //= 2
    a += 1
while X % 5 == 0:
    X //= 5
    b += 1

if X != 1:
    print(-1)
else:
    if a == b == 0:
        while N % 10 == 0:
            N //= 10
        print(N % 10)
    else:
        ans = N % 10
        if a < b:
            ans *= pow(2,b-a,10)
        elif a > b:
            ans *= pow(5,a-b,10)
        print(ans % 10)