hello . i need train to london liverpool street .
{'service': 'train', 'act': 'request', 'slot_name': 'depart', 'value': '?'} {'service': 'train', 'act': 'request', 'slot_name': 'arrive', 'value': '?'} {'service': 'train', 'act': 'request', 'slot_name': 'leave', 'value': '?'}
where are you departing from and do you have a time preference ?