<p>Given an arithmetic equation consisting of positive integers, +, -, * and / (no paren&shy;theses), compute the result.</p>

<p>The expression string contains only non-negative integers, +, -, *, / operators and empty spaces . The integer division should truncate toward zero.</p>

<p><strong>Example&nbsp;1:</strong></p>

<pre>
<strong>Input: </strong>&quot;3+2*2&quot;
<strong>Output:</strong> 7
</pre>

<p><strong>Example 2:</strong></p>

<pre>
<strong>Input:</strong> &quot; 3/2 &quot;
<strong>Output:</strong> 1</pre>

<p><strong>Example 3:</strong></p>

<pre>
<strong>Input:</strong> &quot; 3+5 / 2 &quot;
<strong>Output:</strong> 5
</pre>

<p><strong>Note:</strong></p>

<ul>
	<li>You may assume that the given expression is always valid.</li>
	<li>Do not use the eval built-in library function.</li>
</ul>