Client need the Causal leave carry like this

Hi To All

My Client asked the Causal Leave are 12 per annum.

if i used 2 leave.so the remainng leaves should be carry forward .So next year will be 10 Days,Ok.

Now Client need in 1 st Month its has to shown all the leaves if he wont use those leaves than Half of the leaves should be close.That means he can eligable for 5 leaves on FEB.and MARCH 2,50 Days

End of three months all leaves cant be useful;

How to CONFIGURE?