On 4 January 2016, Barcelona's transfer ban ended. The same day, they registered 77 players across all categories and ages, and both last summer signings Arda Turan and Aleix Vidal became eligible to play with the first team. On 10 February, qualifying for the sixth Copa del Rey final in the last eight seasons, Luis Enrique’s Barcelona broke the club's record of 28 consecutive games unbeaten in all competitions set by Guardiola’s team in the 2010–11 season, with a 1–1 draw with Valencia in the second leg of the 2015–16 Copa del Rey.

Answer this question, if possible (if impossible, reply "unanswerable"): How many players did Barcelona list on the day their transfer ban ended?
77