<?php

error_reporting(-1);

$input = '2-2*4+15-0/1.5=';

$number = 0;
$result = 0;
$op = '';

$numbersAndOperations = array();
preg_match_all('/\d+\.?\d*|[+\-*\/=]/', $input, $numbersAndOperations);

foreach ($numbersAndOperations[0] as $chars) {

	if ($chars == '-' or $chars == '+' or $chars == '*' or $chars == '/' or $chars == '=') {

		$op = $chars;
		
		if (!$result) {
			$result = $number;
		}

	} else {

		$number = floatval($chars);

		if ($op) {

			switch ($op) {
				case '-':
					$result -= $number;
					break;
				case '+':
					$result += $number;
					break;
				case '*':
					$result *= $number;
					break;
				case '/':
					$result /= $number;
					break;
			}

			$number = 0;
		}
		
	}

	if ($op == '=') {
		echo round($result, 2);
		exit();
	}

}