input: Write a Python function which accepts a positive integer `days` representing the total number of days an employee is available for work (starting from day 1) and a 2D array `meetings` where each sub-array represents the start and end days of a specific meeting. The function should return the total count of days when the employee is free and has no meetings scheduled. The meetings may overlap.
  
  Examples:
  >>> days = 10, meetings = [[5, 7], [1, 3], [9, 10]]
  2
  >>> days = 5, meetings = [[2, 4], [1, 3]]
  1
  
  Constraints:
  1 <= days <= 10^9
  1 <= len(meetings) <= 10^5
  meetings[i].length == 2
  1 <= meetings[i][0] <= meetings[i][1] <= days
output: def count_free_days(days, meetings):
      booked = set()
      for start, end in meetings:
          for day in range(start, end + 1):
              booked.add(day)
      return days - len(booked)