instruction: what are the cheapest flights from DENVER to PITTSBURGH that stop in ATLANTA
response: SELECT DISTINCT flight.flight_id FROM airport_service AS AIRPORT_SERVICE_0, airport_service AS AIRPORT_SERVICE_1, airport_service AS AIRPORT_SERVICE_2, city AS CITY_0, city AS CITY_1, city AS CITY_2, fare, flight, flight_fare, flight_stop WHERE ((CITY_1.city_code = AIRPORT_SERVICE_1.city_code AND CITY_1.city_name = 'PITTSBURGH' AND CITY_2.city_code = AIRPORT_SERVICE_2.city_code AND CITY_2.city_name = 'ATLANTA' AND flight_stop.stop_airport = AIRPORT_SERVICE_2.airport_code AND flight.flight_id = flight_stop.flight_id AND flight.to_airport = AIRPORT_SERVICE_1.airport_code) AND CITY_0.city_code = AIRPORT_SERVICE_0.city_code AND CITY_0.city_name = 'DENVER' AND flight.from_airport = AIRPORT_SERVICE_0.airport_code) AND fare.one_direction_cost = (SELECT MIN(FAREalias1.one_direction_cost) FROM airport_service AS AIRPORT_SERVICEalias3, airport_service AS AIRPORT_SERVICEalias4, airport_service AS AIRPORT_SERVICEalias5, city AS CITYalias3, city AS CITYalias4, city AS CITYalias5, fare AS FAREalias1, flight AS FLIGHTalias1, flight_fare AS FLIGHT_FAREalias1, flight_stop AS FLIGHT_STOPalias1 WHERE (CITYalias4.city_code = AIRPORT_SERVICEalias4.city_code AND CITYalias4.city_name = 'PITTSBURGH' AND CITYalias5.city_code = AIRPORT_SERVICEalias5.city_code AND CITYalias5.city_name = 'ATLANTA' AND FLIGHT_STOPalias1.stop_airport = AIRPORT_SERVICEalias5.airport_code AND FLIGHTalias1.flight_id = FLIGHT_STOPalias1.flight_id AND FLIGHTalias1.to_airport = AIRPORT_SERVICEalias4.airport_code) AND CITYalias3.city_code = AIRPORT_SERVICEalias3.city_code AND CITYalias3.city_name = 'DENVER' AND FLIGHT_FAREalias1.fare_id = FAREalias1.fare_id AND FLIGHTalias1.flight_id = FLIGHT_FAREalias1.flight_id AND FLIGHTalias1.from_airport = AIRPORT_SERVICEalias3.airport_code) AND flight_fare.fare_id = fare.fare_id AND flight.flight_id = flight_fare.flight_id