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 l = ["dream"; "dreamer"; "erase"; "eraser"]

let has_suffix s suffix =
  let lens = String.length s in
  let len_suf = String.length suffix in
  if lens < len_suf then false
  else String.sub s (lens - len_suf) len_suf = suffix

let trim_suffix s suffix =
  let lens = String.length s in
  let len_suf = String.length suffix in
  String.sub s 0 (lens - len_suf)

let rec f s =
  if s = "" then "YES"
  else
    match List.filter (has_suffix s) l with
    | [] -> "NO"
    | suf -> f (trim_suffix s (List.hd suf))

let () = f (read_line ()) |> print_endline