from math import floor,ceil

input_file = "input.txt"

seats = []

with open(input_file) as boardings:
    line = boardings.readline()
    while line and line != "\n":
        row_start = 0
        row_end = 127
        column_start = 0
        column_end = 7

        for character in line:
            if character == "F":
                row_end = floor((row_start+row_end)/2)
            elif character == "B":
                row_start = ceil((row_start+row_end)/2)
            elif character == "L":
                column_end = floor((column_start+column_end)/2)
            elif character == "R":
                column_start = ceil((column_start+column_end)/2)
            else: # End of line
                seats.append(row_end*8+column_end)

        line = boardings.readline()

print(f"Highest seat ID : {max(seats)}")


seats.sort()
possible_seats = list(range(seats[0], seats[-1]+1))

# There might be missing seats at the front or the back of the plane
# thus, if we sort and create a range between the smallest and largest ID
# and iterate over both, the number missing in the full range would be our seat.

for i in range(len(seats)):
    if seats[i] != possible_seats[i]:
        print(f"Your seat is {possible_seats[i]}")
        break