import math
n = int(input())
m = int(input())
g = math.gcd(n, m)
n //= g
m //= g
cnt2, cnt5 = 0, 0

while m%2 == 0:
    cnt2 += 1
    m //= 2
    
while m%5 == 0:
    cnt5 += 1
    m //= 5
    
if m > 1:
    print(-1)
else:
    while n%10 == 0:
        n //= 10
    if cnt2 == cnt5:
        print(n%10)
    elif cnt2 > cnt5:
        cnt2 -= cnt5
        for _ in range(cnt2):
            n *= 5
            while n%10 == 0:
                n //= 10
        print(n%10)
    else:
        cnt5 -= cnt2
        for _ in range(cnt5):
            n *= 2
            while n%10 == 0:
                n //= 10
        print(n%10)