Problem:
Score : 300 points

Problem Statement

You are given a string S consisting of lowercase English letters.
Another string T is initially empty.
Determine whether it is possible to obtain S = T by performing the following operation an arbitrary number of times:

Append one of the following at the end of T: dream, dreamer, erase and eraser.

Constraints

1≦|S|≦10^5

S consists of lowercase English letters.

Input

The input is given from Standard Input in the following format:

S

Output

If it is possible to obtain S = T, print YES. Otherwise, print NO.

Sample Input 1

erasedream

Sample Output 1

YES

Append erase and dream at the end of T in this order, to obtain S = T.

Sample Input 2

dreameraser

Sample Output 2

YES

Append dream and eraser at the end of T in this order, to obtain S = T.

Sample Input 3

dreamerer

Sample Output 3

NO

Solution in OCaml (4.02.3) (judge verdict: Accepted)

let list_of_str s =
  let rec f i = if i >= String.length s then [] else s.[i] :: f (i+1) in f 0

let rec solve = function
  | [] -> "YES"
  (* 1. erase[r] はその場で消費して OK *)
  | 'e'::'r'::'a'::'s'::'e'::'r'::xs
  | 'e'::'r'::'a'::'s'::'e'::xs
  (* 2. dreamer... と来ても実は dream erase[r] かもしれない*)
  | 'd'::'r'::'e'::'a'::'m'::'e'::'r'::'a'::'s'::'e'::'r'::xs
  | 'd'::'r'::'e'::'a'::'m'::'e'::'r'::'a'::'s'::'e'::xs
  (* 3. dream[er] *)
  | 'd'::'r'::'e'::'a'::'m'::'e'::'r'::xs
  | 'd'::'r'::'e'::'a'::'m'::xs -> solve xs
  (* 4. NO *)
  | _ -> "NO"

let () = Scanf.scanf "%s" list_of_str |> solve |> print_endline