<?php

interface ShapeInterface
{
    public function area(): int;
}

class Rectangle implements ShapeInterface
{
    private $a;
    private $b;

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

    public function area(): int
    {
        return $this->a * $this->b;
    }
}

class Triangle implements ShapeInterface
{
    private $r;

    public function __construct($r)
    {
        $this->r = $r;
    }

    public function area(): int
    {
        return pi() * pow($this->r, 2);
    }
}