i am going to cambridge and i need a train that leaves on wednesday .
{'service': 'train', 'act': 'request', 'slot_name': 'depart', 'value': '?'} {'service': 'train', 'act': 'request', 'slot_name': 'arrive', 'value': '?'}
where will you be departing from and what time do you need to arrive in cambridge ?