function getSoin(v)
  local t = {}
  while(1 < v) do
    for i = 1, v, 2 do
      ia = (i == 1 and 2 or i) --2, 3, 5, 7, 9, ...
      if(v % ia == 0) then
        if(t[ia] == nil) then t[ia] = 1 else t[ia] = t[ia] + 1 end
        v = v / ia
        break
      end
    end
  end
  return t
end

n, k = io.read("*n", "*n")
soin_n = getSoin(n)

tmp_i = 0
minval = 1
for soin, cnt in pairs(soin_n) do
  if(k <= tmp_i + cnt) then
    for i = 1, k - tmp_i do
      minval = minval * soin
    end
    break
  else
    for i = 1, cnt do
      minval = minval * soin
    end
    tmp_i = tmp_i + cnt
  end
end

result_j = 1
result_cnt = 0
for j = minval, n - 2 do
  soin_j = getSoin(j)
  cnt = 0
  totcnt = 1
  for key, val in pairs(soin_j) do
    totcnt = totcnt * (val + 1)
    if(soin_n[key] ~= nil) then
      cnt = cnt + math.min(soin_n[key], val)
    end
  end
  if(k <= cnt) then
    if(result_cnt < totcnt) then
      result_j = j
      result_cnt = totcnt
    end
  end
end
print(result_j)