def is_valid_num(num):
  NUMBERS = ["0","1","2","3","4","5","6","7","8","9"]
  SIGNS = ["+","-"]
  for i in range(len(num)):
    if i==0:
      if num[i] not in SIGNS+NUMBERS:
        return False
    elif num[i] not in NUMBERS:
      return False

  return True

print("""
Available Seats: 50
Business Class: Rs.15000 per seat
Economy Class: Rs.7500 per seat
""")

TOTAL_SEAT = 50
remaining_seat=50

while True:
  seat_type = input("Enter class (Business|Economy) for reservation:\n")
  if seat_type != "Business" and seat_type != "Economy":
    print("Invalid class choice. Please enter Business or Economy.")
    continue

  per_seat_cost=7500
  if seat_type=="Business":
    per_seat_cost = 15000

  num_seat = input("Enter the number of seats to reserve: ")
  if not is_valid_num(num_seat):
    print("Invalid input. Please enter a valid number.")
    continue

  if int(num_seat)>remaining_seat:
    print(f"Invalid number of seats. Available seats: {remaining_seat}")
  else:
    num_seat = int(num_seat)
    remaining_seat-=num_seat

    print(f"Reservation successful! Total cost: Rs.{num_seat*per_seat_cost}")

  reserve_again = input("Do you want to make another reservation?\n(yes|no): ")
  if reserve_again == "yes":
    continue
  else:
    break

print("Boarding Passes:")
for i in range(TOTAL_SEAT-remaining_seat):
  print(f"Seat {i+1} - Boarding Pass")

print("Thank you for using our reservation system!")