input_rut = '8909201-9'
tmp = input_rut.split('-')
rut = tmp[0]
dv = tmp[1]

reverse = rut.reverse
index = 0
factor = 2
suma = 0
while index < reverse.length do
  suma += reverse[index].to_i * factor

  factor += 1
  if factor > 7
    factor = 2
  end

  index += 1
end

resto = 11 - (suma % 11)

dv_pulento = -1
if resto >= 1 && resto <= 9
  dv_pulento = resto
elsif resto == 11
  dv_pulento = 0
elsif resto == 10
  dv_pulento = 'k'
end

puts dv_pulento