How to restrict the Casual leaves and Sick leaves in continuesly in infotye 2001 in pa30

Hi Experts,

                In pa30 transaction with infotype is 2001 and subtype is cl01 or sl01 , when i am assigning leave type (cl01 or sl01) first check before leave is ( sl01 or cl01) at that time i want to throw an error message and the date range is varying. can you help me about this logic it's urgent requirement i am new to ABAP/HR.