In 2005, the Astros started poorly and found themselves with a 15–30 record in late May. The Houston Chronicle had written them off with a tombstone emblazoned with "RIP 2005 Astros". However, from that low point until the end of July, Houston went 42–17 and found themselves in the lead for an NL wild card spot. July saw the best single-month record in the clubs history at 22-7. Offensive production had increased greatly after a slow start in the first two months.  The Astros had also developed an excellent pitching staff, anchored by Roy Oswalt (20–12, 2.94), Andy Pettitte (17–9, 2.39), and Roger Clemens (13–8 with a league-low ERA of only 1.87). The contributions of the other starters—Brandon Backe (10–8, 4.76) and rookie starters Ezequiel Astacio (3–6, 5.67) and Wandy Rodríguez (10–10, 5.53)—were less remarkable, but enough to push the Astros into position for a playoff run. The Astros won a wild card berth on the final day of the regular season, becoming the first team since the world champion 1914 Boston Braves to qualify for the postseason after being 15 games under .500.
Question: How many people were on the pitching staff?
Answer: 6