what is the cheapest one way fare from san francisco to boston on wednesday august twenty first
O O O B-cost_relative B-round_trip I-round_trip O O B-fromloc.city_name I-fromloc.city_name O B-toloc.city_name O B-depart_date.day_name B-depart_date.month_name B-depart_date.day_number I-depart_date.day_number