local ffi = require("ffi")
local C = ffi.C
ffi.cdef[[
long long atoll(const char*);
]]

local function lltonumber(str)
  return C.atoll(str)
end

local n = io.read()
n = lltonumber(n)
local m = io.read()
m = lltonumber(m)

while m % 10LL == 0LL do
  m = m / 10LL
end
while n % 10LL == 0LL do
  n = n / 10LL
end

while n % 2LL == 0LL and m % 2LL == 0LL do
  n = n / 2LL
  m = m / 2LL
end
while n % 5LL == 0LL and m % 5LL == 0LL do
  n = n / 5LL
  m = m / 5LL
end
local m2, m5 = 0, 0
while m % 2LL == 0LL do
  m2 = m2 + 1
  m = m / 2LL
end
while m % 5LL == 0LL do
  m5 = m5 + 1
  m = m / 5LL
end
if n % m ~= 0LL then
  print(-1)
  os.exit()
end
n = n / m
if 0LL < m2 then
  print(5)
  os.exit()
end
n = n % 10LL
n = tostring(n):gsub("LL", "")
n = tonumber(n)
for i = 1, m5 do
  n = (n * 2) % 10
end
print(n)