<p>A child is running up a staircase with n steps and can hop either 1 step, 2 steps, or 3 steps at a time. Implement a method to count how many possible ways the child can run up the stairs.&nbsp;The result may be large, so return it modulo 1000000007.</p>



<p><strong>Example1:</strong></p>



<pre>

<strong> Input</strong>: n = 3 

<strong> Output</strong>: 4

</pre>



<p><strong>Example2:</strong></p>



<pre>

<strong> Input</strong>: n = 5

<strong> Output</strong>: 13

</pre>



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



<ol>

	<li><code>1 &lt;= n &lt;= 1000000</code></li>

</ol>