cal = (1..31).map { |i| i }
sum_day = cal.map  do |d|
  if d < 10
    d
  elsif d >= 10
    d / 10 + d % 10
  end
end

count = 0
(1..12).each do |x|
  y = sum_day.select { |n| n == x }
  count += y.length
end

p count