<?php

class Drink
{

    public $num = 5;

    public $topUnit = 4;

    public $bottleUnit = 2;

    public $leftTop;

    public $leftBottle;

    public $sum = 0;

    public function __construct()
    {
        $this->sum = $this->num + $this->cal($this->num, $this->num);
    }

    public function cal($top, $bottle)
    {
        if ($top >= $this->topUnit || $bottle >= $this->bottleUnit) {
            $this->leftTop = intval($top / $this->topUnit) + $top % $this->topUnit + intval($bottle / $this->bottleUnit);
            $this->leftBottle = intval($bottle / $this->bottleUnit) + $bottle % $this->bottleUnit + intval($top / $this->topUnit);
            $this->sum = intval($top / $this->topUnit) + intval($bottle / $this->bottleUnit) + $this->cal($this->leftTop, $this->leftBottle);
            
            return $this->sum;
        } else {
            return 0;
        }
    }

    public function __toString()
    {
        return (string) $this->sum;
    }
}

$c = new Drink();
echo $c;