How many days after the Bulgarians entered Prokuplje did the Hungarians enter Kursumlija?
return Bulgarians entered Prokuplje ;return Hungarians did enter Kursumlija ;return when  was  #1 ;return when  was  #2 ;return difference of #3 and  #4 in  days
['select', 'select', 'project', 'project', 'arithmetic']