Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Driver | Constructor | Laps | Time/Retired | Grid |
| --- | --- | --- | --- | --- |
| Johnny Herbert | Stewart - Ford | 66.0 | 1:41:54.314 | 14.0 |
| Jarno Trulli | Prost - Peugeot | 66.0 | +22.619 | 10.0 |
| Rubens Barrichello | Stewart - Ford | 66.0 | +22.866 | 15.0 |
| Ralf Schumacher | Williams - Supertec | 66.0 | +39.508 | 4.0 |
| Mika Häkkinen | McLaren - Mercedes | 66.0 | +1:02.950 | 3.0 |
| Marc Gené | Minardi - Ford | 66.0 | +1:05.154 | 20.0 |
| Eddie Irvine | Ferrari | 66.0 | +1:06.683 | 9.0 |
| Ricardo Zonta | BAR - Supertec | 65.0 | +1 lap | 17.0 |
| Olivier Panis | Prost - Peugeot | 65.0 | +1 lap | 5.0 |
| Jacques Villeneuve | BAR - Supertec | 61.0 | Clutch | 8.0 |
| Luca Badoer | Minardi - Ford | 53.0 | Gearbox | 19.0 |
| Pedro de la Rosa | Arrows | 52.0 | Gearbox | 22.0 |
| Giancarlo Fisichella | Benetton - Playlife | 48.0 | Spun off | 6.0 |
| Mika Salo | Ferrari | 44.0 | Brakes | 12.0 |
| Toranosuke Takagi | Arrows | 42.0 | Accident | 21.0 |
| David Coulthard | McLaren - Mercedes | 37.0 | Spun off | 2.0 |
| Jean Alesi | Sauber - Petronas | 35.0 | Halfshaft | 16.0 |
| Heinz-Harald Frentzen | Jordan - Mugen-Honda | 32.0 | Electrical | 1.0 |
| Alessandro Zanardi | Williams - Supertec | 10.0 | Collision | 18.0 |
| Damon Hill | Jordan - Mugen-Honda | 0.0 | Electrical | 7.0 |
| Alexander Wurz | Benetton - Playlife | 0.0 | Collision | 11.0 |
| Pedro Diniz | Sauber - Petronas | 0.0 | Collision | 13.0 |
Question:
what is the sum of laps when grid is less than 20 and johnny herbert is driving?
Answer:
66.0