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 | Young rider classification | Team classification | Combativity award |
| --- | --- | --- | --- | --- | --- | --- | --- |
| 1.0 | Fabian Cancellara | Fabian Cancellara | Fabian Cancellara | Alberto Contador | Roman Kreuziger | Astana | no award |
| 2.0 | Mark Cavendish | Fabian Cancellara | Mark Cavendish | Jussi Veikkanen | Roman Kreuziger | Astana | Stef Clement |
| 3.0 | Mark Cavendish | Fabian Cancellara | Mark Cavendish | Jussi Veikkanen | Tony Martin | Astana | Samuel Dumoulin |
| 4.0 | Astana | Fabian Cancellara | Mark Cavendish | Jussi Veikkanen | Tony Martin | Astana | no award |
| 5.0 | Thomas Voeckler | Fabian Cancellara | Mark Cavendish | Jussi Veikkanen | Tony Martin | Astana | Mikhail Ignatiev |
| 6.0 | Thor Hushovd | Fabian Cancellara | Mark Cavendish | Stéphane Augé | Tony Martin | Astana | David Millar |
| 7.0 | Brice Feillu | Rinaldo Nocentini | Mark Cavendish | Brice Feillu | Tony Martin | Astana | Christophe Riblon |
| 8.0 | Luis León Sánchez | Rinaldo Nocentini | Thor Hushovd | Christophe Kern | Tony Martin | Ag2r-La Mondiale | Sandy Casar |
| 9.0 | Pierrick Fédrigo | Rinaldo Nocentini | Thor Hushovd | Egoi Martínez | Tony Martin | Ag2r-La Mondiale | Franco Pellizotti |
| 10.0 | Mark Cavendish | Rinaldo Nocentini | Thor Hushovd | Egoi Martínez | Tony Martin | Ag2r-La Mondiale | Thierry Hupond |
| 11.0 | Mark Cavendish | Rinaldo Nocentini | Mark Cavendish | Egoi Martínez | Tony Martin | Ag2r-La Mondiale | Johan Van Summeren |
| 12.0 | Nicki Sørensen | Rinaldo Nocentini | Mark Cavendish | Egoi Martínez | Tony Martin | Team Saxo Bank | Nicki Sørensen |
| 13.0 | Heinrich Haussler | Rinaldo Nocentini | Thor Hushovd | Franco Pellizotti | Tony Martin | Team Saxo Bank | Heinrich Haussler |
| 14.0 | Sergei Ivanov | Rinaldo Nocentini | Thor Hushovd | Franco Pellizotti | Tony Martin | Ag2r-La Mondiale | Martijn Maaskant |
| 15.0 | Alberto Contador | Alberto Contador | Thor Hushovd | Franco Pellizotti | Andy Schleck | Astana | Simon Špilak |
| 16.0 | Sandy Casar * | Alberto Contador | Thor Hushovd | Franco Pellizotti | Andy Schleck | Astana | Franco Pellizotti |
| 17.0 | Fränk Schleck | Alberto Contador | Thor Hushovd | Franco Pellizotti | Andy Schleck | Astana | Thor Hushovd |
| 18.0 | Alberto Contador | Alberto Contador | Thor Hushovd | Franco Pellizotti | Andy Schleck | Astana | no award |
| 19.0 | Mark Cavendish | Alberto Contador | Thor Hushovd | Franco Pellizotti | Andy Schleck | Astana | Leonardo Duque |
| 20.0 | Juan Manuel Gárate | Alberto Contador | Thor Hushovd | Franco Pellizotti | Andy Schleck | Astana | Tony Martin |
| 21.0 | Mark Cavendish | Alberto Contador | Thor Hushovd | Franco Pellizotti | Andy Schleck | Astana | Fumiyuki Beppu |
Question:
Who won stage 18?
Answer:
Alberto Contador