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:
| Stage | Winner | General classification | Points classification | Mountains classification | Combination classification | Team classification |
| --- | --- | --- | --- | --- | --- | --- |
| 1.0 | ONCE-Eroski | Joseba Beloki | no award | no award | Joseba Beloki | ONCE-Eroski |
| 2.0 | Danilo di Luca | Joseba Beloki | Danilo di Luca | Mederic Clain | Vitoriano Fernandez | ONCE-Eroski |
| 3.0 | Mario Cipollini | Joseba Beloki | Erik Zabel | Mederic Clain | Mederic Clain | ONCE-Eroski |
| 4.0 | Mario Cipollini | Joseba Beloki | Erik Zabel | Mederic Clain | Vitoriano Fernandez | ONCE-Eroski |
| 5.0 | Guido Trentin | Mikel Zarrabeitia | Erik Zabel | Mederic Clain | Guido Trentin | ONCE-Eroski |
| 6.0 | Roberto Heras | Óscar Sevilla | Erik Zabel | Mederic Clain | Félix Garcia | ONCE-Eroski |
| 7.0 | Mario Cipollini | Óscar Sevilla | Erik Zabel | Mederic Clain | Félix Garcia | ONCE-Eroski |
| 8.0 | Aitor González | Óscar Sevilla | Erik Zabel | Gilberto Simoni | Óscar Sevilla | ONCE-Eroski |
| 9.0 | Pablo Lastras | Óscar Sevilla | Erik Zabel | Gilberto Simoni | Óscar Sevilla | ONCE-Eroski |
| 10.0 | Aitor González | Óscar Sevilla | Erik Zabel | Gilberto Simoni | Óscar Sevilla | Kelme-Costa Blanca |
| 11.0 | Pablo Lastras | Óscar Sevilla | Erik Zabel | Gilberto Simoni | Óscar Sevilla | Kelme-Costa Blanca |
| 12.0 | Alessandro Petacchi | Óscar Sevilla | Erik Zabel | Gilberto Simoni | Óscar Sevilla | Kelme-Costa Blanca |
| 13.0 | Giovanni Lombardi | Óscar Sevilla | Erik Zabel | Gilberto Simoni | Óscar Sevilla | Team Coast |
| 14.0 | Sergei Smetanine | Óscar Sevilla | Erik Zabel | Gilberto Simoni | Óscar Sevilla | Team Coast |
| 15.0 | Roberto Heras | Roberto Heras | Erik Zabel | Gilberto Simoni | Roberto Heras | Kelme-Costa Blanca |
| 16.0 | Santiago Botero | Roberto Heras | Erik Zabel | Aitor Osa | Roberto Heras | Kelme-Costa Blanca |
| 17.0 | Angelo Furlan | Roberto Heras | Erik Zabel | Aitor Osa | Roberto Heras | Kelme-Costa Blanca |
| 18.0 | Santiago Blanco | Roberto Heras | Erik Zabel | Roberto Heras | Roberto Heras | Kelme-Costa Blanca |
| 19.0 | Jose Vicente Garcia Acosta | Roberto Heras | Erik Zabel | Aitor Osa | Roberto Heras | Kelme-Costa Blanca |
| 20.0 | Angelo Furlan | Roberto Heras | Erik Zabel | Aitor Osa | Roberto Heras | Kelme-Costa Blanca |
| 21.0 | Aitor González | Aitor González | Erik Zabel | Aitor Osa | Roberto Heras | Kelme-Costa Blanca |
Question:
what is the minimum stage where mountains classification is aitor osa and aitor gonzález won?
Answer:
21.0