from math import gcd, sqrt
def Fraction(A, B):
    G = gcd(A, B)
    return A // G, B // G

def PrimeFactorization(N):
    ret = []
    for i in range(2,int(sqrt(N))+1):
        while N % i == 0:
            ret.append(i)
            N //= i
    if N > 1:
        ret.append(N)
    return ret

N = int(input())
M = int(input())
N,M = Fraction(N, M)
P = PrimeFactorization(M)
T = 0
F = 0
for i in P:
    if i != 2 and i != 5:
        print(-1)
        exit()
    if i == 2:
        T += 1
    else:
        F += 1
while T > F:
    N *= 5
    T -= 1
while T < F:
    N *= 2
    F -= 1
while N % 10 == 0:
    N //= 10
print(N % 10)