How to get Top 1 with below statement

Question

Hi

  In below statement i want to get Top 1 record

CASE
    WHEN (
        SELECT COUNT(*)
        FROM SessionDeliveryParticipant AS sub
        WHERE sub.[SessionDeliveryCalendarID] = [SessionDeliveryCalendarID]
        AND sub.PresentInSession = 0
    ) = COUNT(*) THEN 1
    ELSE 0 End

Thanks