def SeatingStudents(arr):
K = arr[0]
occupied = arr[1:]
rows = int(K/2)
seats = []
x = 0
for i in range(rows):
seats.append([])
for j in range(2):
if((x+1) in occupied):
full_seat = True
else:
full_seat = False
seats[i].append(str(full_seat))
x+=1
seating = 0
for i in range(rows-1):
if((seats[i][0] == str(False)) and (seats[i][1] == str(False))):
seating+=1
if((seats[i][0] == str(False)) and (seats[i+1][0] == str(False))):
seating+=1
if((seats[i][1] == str(False)) and (seats[i + 1][1] == str(False))):
seating+=1
if((seats[rows - 1][0] == str(False)) and (seats[rows - 1][1] == str(False))):
seating+=1
return seating
print(SeatingStudents([12, 2, 6, 7, 11]))