import strutils,math

var
    N = stdin.readline.parseBiggestInt
    M = stdin.readline.parseBiggestInt
    s = gcd(N,M)
    cnt2,cnt5 : int
    n : string
N = N div s
M = M div s
var M2 = M

while M mod 2 == 0:
    M = M div 2
    cnt2 += 1

while M mod 5 == 0:
    M = M div 5
    cnt5 += 1
if M == 1:
    if (N.float64 / M2.float64) mod 1.0 == 0.0:
        var j = 10.0
        var a = (N.float64 / M2.float64) mod j
        while a == 0.0:
            j *= 10.0
            a = (N.float64 / M2.float64) mod j
        n = $a
        echo n[0]
    else:
        for i in 0..cnt5:
            while N mod 10 == 0:
                N = N div 10
            N = N mod 100
            N *= 2
        for i in 0..cnt2:
            while N mod 10 == 0:
                N = N div 10
            N = N mod 100
            N *= 5
        while N mod 10 == 0:
            N = N div 10
        n = $N
        echo n[^1]
else:
    echo -1