How much is the average build up play speed of the Heart of Midlothian team?
Heart of Midlothian refers to team_long_name = 'Heart of Midlothian'; average build up play speed refers to  AVG(buildUpPlaySpeed)
SELECT CAST(SUM(t2.buildUpPlaySpeed) AS REAL) / COUNT(t2.id) FROM Team AS t1 INNER JOIN Team_Attributes AS t2 ON t1.team_api_id = t2.team_api_id WHERE t1.team_long_name = 'Heart of Midlothian'