<?php
    list($l, $k) = explode(" ", trim(fgets(STDIN)));
    
    $bite = floor($l / ($k * 2));
    if($bite < 1){
        $bite = 0;
    }
    $nokori = $l - ($k * 2) * $bite;
    $count = $bite;
    while($nokori > ($k * 2)){
    $nokori = $nokori - ($k * 2);
    $count++;
    }
    echo $count * $k;
?>