public const A_FACTOR = 100;
    public const B_FACTOR = 10;
    public const C_FACTOR = 1;

    private int $a;
    private int $b;
    private int $c;

    public function __construct(int $a, int $b, int $c)
    {
        $this->a = $a;
        $this->b = $b;
        $this->c = $c;
    }

    public function plus(self $specificity): self
    {
        return new self($this->a + $specificity->a, $this->b + $specificity->b, $this->c + $specificity->c);
    }

    public function getValue(): int
    {
        return $this->a * self::A_FACTOR + $this->b * self::B_FACTOR + $this->c * self::C_FACTOR;
    }

    /**
     * Returns -1 if the object specificity is lower than the argument,
     * 0 if they are equal, and 1 if the argument is lower.
     */
    public function compareTo(self $specificity): int
    {
        if ($this->a !== $specificity->a) {
            return $this->a > $specificity->a ? 1 : -1;
        }

        if ($this->b !== $specificity->b) {
            return $this->b > $specificity->b ? 1 : -1;
        }

        if ($this->c !== $specificity->c) {
            return $this->c > $specificity->c ? 1 : -1;
        }

        return 0;
    }
}