Table:
text: 1994 French motorcycle Grand Prix
250 cc classification
250 cc classification
Pos Rider Manufacturer Time_Retired Points_
17 Adolf Stadler Honda +1:16.427 
18 Juan Borja Honda +1:19.607 
19 Chrisrian Boudinot Aprilia +1:20.163 
20 Bernd Kassner Aprilia +1:20.761 
21 Andreas Preining Aprilia +1:26.864 
22 Noel Ferro Honda +1:27.009 
23 Sebastien Scarnato Honda +1:36.321 
24 Krisse Kaas Yamaha +1 Lap 
25 Donnie Hough Honda +1 Lap 
Ret Rodney Fee Honda Retirement 
Ret Jurgen vd Goorbergh Aprilia Retirement 
Ret Luis D`Antin Honda Retirement 
Ret Manuel Hernandez Aprilia Retirement 
Ret Frederic Protat Honda Retirement 
Ret Giuseppe Fiorillo Honda Retirement 
Ret José Luis Cardoso Aprilia Retirement 
Ret Enrique de Juan Aprilia Retirement 
Ret Alessandro Gramigni Aprilia Retirement 

text: 1994 French motorcycle Grand Prix
250 cc classification
250 cc classification
Pos Rider Manufacturer Time_Retired Points_
1 Loris Capirossi Honda 43:06.089 25
2 Doriano Romboni Honda +0.689 20
3 Max Biaggi Aprilia +1.181 16
4 Ralf Waldmann Honda +5.123 13
5 Jean-Michel Bayle Aprilia +5.528 11
6 Nobuatsu Aoki Honda +5.821 10
7 Jean Philippe Ruggia Aprilia +9.018 9
8 Tetsuya Harada Yamaha +24.059 8
9 Tadayuki Okada Honda +29.043 7
10 Wilco Zeelenberg Honda +36.273 6
11 Toshihiko Honma Yamaha +41.787 5
12 Adrien Bosshard Honda +52.489 4
13 Carlos Checa Honda +57.206 3
14 Eskil Suter Aprilia +1:01.503 2
15 Luis Maurel Honda +1:03.353 1
16 Patrick vd Goorbergh Aprilia +1:04.277

Question: How many riders altogether rode a Yamaha motorcycle at the 1994 French motorcycle Grand Prix?