context: They have a very strong record in home games, with Georgios Karaiskakis Stadium being one of the most fearsome and strong home grounds in Europe. This has been proved by some long-standing unbeaten sequences, with Olympiacos staying unbeaten for 15 straight Champions League matches, with Manchester United being the first team to beat Olympiacos at home, in the latters fifth consecutive participation in the tournament with its new format. Furthermore, Olympiacos won 15 of their 19 UEFA Champions League games at home from 2009–10 UEFA Champions League to 2014–15 UEFA Champions League. They have an impressive record of wins at home in the European Cup/UEFA Champions League against the greatest clubs in European football, having beaten Real Madrid F.C. (2–1), Liverpool F.C. (1–0), Manchester United F.C. (2–0), AFC Ajax (2–0, 1–0), Juventus F.C. (1–0), Arsenal F.C. (1–0, 3–1, 2–1), FC Porto (1–0, 2–1, 1–0), S.L. Benfica (1–0, 1–0), Valencia CF (1–0), Borussia Dortmund (3–1), Atlético Madrid (3–2), Bayer 04 Leverkusen (6–2), AS Monaco FC (1–0), Celtic F.C. (2–0), Olympique Lyonnais (2–1), R.S.C. Anderlecht (3–0, 3–1), SV Werder Bremen (3–0) and Deportivo de La Coruña (1–0), among many others.
question: How many UEFA Champions League games at home did the Olympiacos lose during the stretch from 2009-2015?
answer: 4