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 main () =
  let n = Scanf.scanf "%s\n" (fun a -> a) in
  let n = ref @@ BatString.rev n in
  let xs = BatArray.map BatString.rev [|"dream"; "dreamer"; "erase"; "eraser"|] in
  let flag = ref true in
  while !flag do
    flag := BatArray.fold_left (fun acc elm ->
        if BatString.equal (BatString.left !n @@ BatString.length elm) elm
        then (n := BatString.tail !n @@ BatString.length elm; true)
        else acc || false
      ) false xs
  done;
  Printf.printf (if BatString.is_empty !n then "YES" else "NO")

let _ = main ()