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 char_list_of_str s =
  let rec f res i = 
    if i < 0
    then res
    else f (s.[i]::res) @@ i-1
  in
  f [] (String.length s - 1)

let rec solve = function
  | []
      -> "YES"
  | 'e'::'r'::'a'::'s'::'e'::'r'::xs
  | 'e'::'r'::'a'::'s'::'e'::xs
  | 'd'::'r'::'e'::'a'::'m'::'e'::'r'::'a'::'s'::'e'::'r'::xs
  | 'd'::'r'::'e'::'a'::'m'::'e'::'r'::'a'::'s'::'e'::xs
  | 'd'::'r'::'e'::'a'::'m'::'e'::'r'::xs
  | 'd'::'r'::'e'::'a'::'m'::xs
      -> solve xs
  | _ -> "NO"

let () =
  Scanf.scanf "%s\n" char_list_of_str
  |> solve
  |> Printf.printf "%s\n"