number = input()

is_one_digit = (len(number) == 1)
is_two_digit = (len(number) == 2)
is_three_digit = (len(number) == 3)

if is_one_digit:
  print(number)
elif is_two_digit:
  first_digit = int(number[0])
  second_digit = int(number[1])
  print(first_digit + second_digit)
elif is_three_digit:
  first_digit = int(number[0])
  second_digit = int(number[1])
  third_digit = int(number[2])
  print(first_digit + second_digit + third_digit)
else:
  first_digit = int(number[0])
  second_digit = int(number[1])
  third_digit = int(number[2])
  fourth_digit = int(number[3])
  print(first_digit + second_digit + third_digit + fourth_digit)