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)

(* O(|s|) *)
let solve s =
  let rec loop i =
    if i <= 0 then
      "YES"
    else
      let match_size = List.fold_left
        (fun match_size each ->
          if match_size <> 0 then
            match_size
          else
            let len = String.length each in
            if i - len < 0 then
              match_size
            else
              if String.sub s (i - len) len = each then len else match_size)
        0
        ["dream"; "dreamer"; "erase"; "eraser"]
      in
        if match_size = 0 then
          "NO"
        else
          loop (i - match_size)
  in
    loop (String.length s)

let _ = read_line () |> solve |> print_endline