salesforce

how to display only particular number of data from column. E.g i there is 20 data but i want to display only 6 in firstName
here is the code
<apex:page standardController="Lead" recordSetVar="leads">
<apex:pageBlock title="Lead List">
<!-- Lead List -->
<apex:pageBlockTable value="{! leads }" var="ld">
<apex:column value="{! ld.FirstName }"/>
<apex:column value="{! ld.LastName }"/>
<apex:column value="{! ld.Company }"/>
<apex:column value="{! ld.Phone }"/>
</apex:pageBlockTable>
</apex:pageBlock>
</apex:page>