|Pos|No|Driver|Constructor|Laps|Time/Retired|Grid|Points|
|---|---|---|---|---|---|---|---|
|1|5|Fernando Alonso|Renault|56|1:31:33.736|1|10|
|2|16|Jarno Trulli|Toyota|56|+24.327|2|8|
|3|8|Nick Heidfeld|Williams-BMW|56|+32.188|10|6|
|4|10|Juan Pablo Montoya|McLaren-Mercedes|56|+41.631|11|5|
|5|17|Ralf Schumacher|Toyota|56|+51.854|5|4|
|6|14|David Coulthard|Red Bull-Cosworth|56|+1:12.543|8|3|
|7|1|Michael Schumacher|Ferrari|56|+1:19.988|13|2|
|8|15|Christian Klien|Red Bull-Cosworth|56|+1:20.835|7|1|
|9|9|Kimi Räikkönen|McLaren-Mercedes|56|+1:21.580|6||
|10|12|Felipe Massa|Sauber-Petronas|55|+1 Lap|14||
|11|19|Narain Karthikeyan|Jordan-Toyota|54|+2 Laps|17||
|12|18|Tiago Monteiro|Jordan-Toyota|53|+3 Laps|18||
|13|21|Christijan Albers|Minardi-Cosworth|52|+4 Laps|19||
|Ret|2|Rubens Barrichello|Ferrari|49|Handling|12||
|Ret|6|Giancarlo Fisichella|Renault|36|Collision|3||
|Ret|7|Mark Webber|Williams-BMW|36|Collision|4||
|Ret|11|Jacques Villeneuve|Sauber-Petronas|26|Spun Off|16||
|Ret|3|Jenson Button|BAR-Honda|2|Engine|9||
|Ret|4|Anthony Davidson|BAR-Honda|2|Engine|15||
|Ret|20|Patrick Friesacher|Minardi-Cosworth|2|Spun Off|20||

Question: how many drivers ended the race early because of engine problems?
Answer: 2