How many more Moldovan citizens were of Bulgarian ancestry than Serbian citizens with Bulgarian ancestry?
return Moldovan citizens  ;return Serbian citizens  ;return #1 that have Bulgarian  ancestry  ;return #2 that have Bulgarian  ancestry  ;return number of  #3 ;return number of  #4 ;return the  difference of #5 and  #6
['select', 'select', 'filter', 'filter', 'aggregate', 'aggregate', 'arithmetic']