wasp.php

<style>
    div,p{
        display:inline; /*Added to avoid confusion in outpu*/
    }
</style>
<form method="POST">
    <textarea name="html_input" required ><?php echo !empty($_POST['html_input'])?$_POST['html_input']:'';?></textarea>
    <input type="submit">
</form>
<?php
$wrapper = 4;
if(!empty($_POST['html_input']))
{
    $html = explode(PHP_EOL, trim($_POST['html_input']));
    $lines = count($html);
    echo $lines.'<br/><br/>';
    if($lines<=5)
    {
        $wrapper = $lines-1;
        $rem = 0;
        $break_at = 1;
    }
    else if($lines<=15)
    {
        //5, 6, 7, 10, 11, 15
        if(in_array($lines, [6, 7, 10, 11, 15]))
            $break_at = floor($lines/$wrapper);
        else
            $break_at = floor($lines/$wrapper)-1;
        $rem = $lines%5;
    }
    else
    {
        $break_at = floor($lines/$wrapper)-1;
        $rem = ($lines%$wrapper);
    }
    for($i=0,$break=1; $i<$lines; $i++,$break++)
    {
        echo $html[$i].'<br/>';
        if(($break % $break_at ===0) && $wrapper)
        {
            if($rem)
            {
                echo $html[++$i].'<br/>';
                $rem--;
            }
            echo 'Hello<br/>';
            $wrapper--;
        }
    }
}