BeiDou-1 is an experimental regional navigation system, which consists of four satellites (three working satellites and one backup satellite). The satellites themselves were based on the Chinese DFH-3 geostationary communications satellite and had a launch weight of 1,000 kilograms (2,200 pounds) each.
BeiDou-1 consists of four backup satellites and how many working satellites?
{'text': 'three', 'answer_start': 91}