free_meeting_time

def time_sort(time):
  i = 0
  music = time[i][1]
  for music in range(len(time)-1,0,-1):
    for i in range(music):
      if time[i][1]>time[i+1][1]:
          clock = time[i]
          time[i] = time[i+1]
          time[i+1] = clock
  return time

def freetime(time):
	
	sorted_list = time_sort(time)
	print (sorted_list)
	free = []
	if sorted_list[0][0]>0:
		free.append((0,sorted_list[0][0]))
	for i in range(len(sorted_list)-1):
		if sorted_list[i][1] < sorted_list[i+1][0]:
			free.append((sorted_list[i][1], sorted_list[i+1][0]))
	if sorted_list[0][0]>0:
		free.append((sorted_list[-1][1],0))	
	return free	
time = [(18,20), (7,8), (8,10), (13,17)]

print(freetime(time))