Hi all, I try to do the tutorials and in the challenge of "Using simple variables and formulas"have this error:

Challenge not yet complete... here's what's wrong:
The Visualforce page did not fit the criteria. The first name of the logged in user was not output using dynamic global variables.

but my code is:
 

<apex:page sidebar="false">
    
    <apex:pageBlock title="User Status">
        <apex:pageBlockSection columns="1">
        	
            {! $User.FirstName }
            
        </apex:pageBlockSection>
    </apex:pageBlock>
    
</apex:page>