|Pos|Driver|Entrant|Constructor|Time/Retired|Grid|
|---|---|---|---|---|---|
|1|Jim Clark|Team Lotus|Lotus-Climax|2.02:58.6|1|
|2|Richie Ginther|Owen Racing Organisation|BRM|+ 22.6 s|3|
|3|Graham Hill|Owen Racing Organisation|BRM|+ 28.2 s|2|
|4|Jack Brabham|Brabham Racing Organisation|Brabham-Climax|+ 52.0 s|11|
|5|Tony Maggs|Cooper Car Company|Cooper-Climax|72 laps|6|
|6|Bruce McLaren|Cooper|Cooper-Climax|72 laps|7|
|7|Mike Hailwood|Reg Parnell (Racing)|Lola-Climax|70 laps|9|
|8|Ian Burgess|Scirocco-Powell (Racing Cars)|Scirocco-BRM|69 laps|18|
|9|Peter Revson|Reg Parnell (Racing)|Lotus-BRM|69 laps|15|
|10|Carel Godin de Beaufort|Ecurie Maarsbergen|Porsche|67 laps|20|
|11|Jo Siffert|Siffert Racing Team|Lotus-BRM|Engine (66 laps)|12|
|12|André Pilette|André Pilette|Lotus-Climax|63 laps|21|
|13|Innes Ireland|British Racing Partnership|Lotus-BRM|Oil pressure (56 laps)|5|
|14|Bernard Collomb|Bernard Collomb|Lotus-Climax|Oil pressure (46 laps)|19|
|Ret|Ian Raby|Ian Raby (Racing)|Gilby-BRM|Ignition|13|
|Ret|Dan Gurney|Brabham Racing Organisation|Brabham-Climax|Oil leak|16|
|Ret|Mike Beckwith|British Racing Partnership|Lotus-BRM|Accident|17|
|Ret|Masten Gregory|Tim Parnell|Lotus-BRM|Cam follower|14|
|Ret|Trevor Taylor|Team Lotus|Lotus-Climax|Crownwheel & pinion|4|
|Ret|Jo Bonnier|Rob Walker Racing Team|Cooper-Climax|Oil pressure|8|
|Ret|Tony Settember|Scirocco-Powell (Racing Cars)|Scirocco-BRM|Valve gear|22|
|Ret|Bob Anderson|DW Racing Enterprises|Lola-Climax|Gearbox|10|
|WD|Peter Arundell|Team Lotus|Lotus-Climax|Car not ready|-|

Question: how many different drivers are listed?
Answer: 23