import strutils

###
# (ΦωΦ)＜もっといい方法はないかな？
proc mymapII(s:seq[string]):auto= result = (s[0].parseInt, s[1].parseInt)
###

var
  (l, k) = stdin.readLine.split.mymapII

var times = l div (2*k) - int(l mod (2*k) == 0)
echo k * times