i want to go from denver to atlanta round trip and make a stop at pittsburgh may i have the cheapest fare 
return fares ;return #1 from  denver ;return #2 to atlanta ;return #3 that  make a stop at pittsburgh ;return #4 that  are  round trip ;return #5 that  are  cheapest
['select', 'filter', 'filter', 'filter', 'filter', 'filter']