Selenium get element in C#

I'm trying to get number in small tag in HTML

Html code:

...

<div class="form-group col-sm-12">
    <label>Amount</label>
    <input type="number" name="amount" class="form-control" placeholder="10" value="10">
    <small class="form-text text-muted">Max Amount: 2000</small>
</div>

...

this code I have written returns null. I want to get 2000 number in the element.