let _ =
  let arr = Array.map (fun n -> (n, (n mod 10) + (n / 10)))
                      (Array.init 31 (fun n -> n + 1)) in
  let happy_days = Array.fold_left (fun a (d, s) ->
                       if (s = 4 || s = 6 || s = 9 || s = 11) && 30 < d then
                         a
                       else
                         a + 1
                     ) 0 arr
  in
  print_int (happy_days); print_newline ();;