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 Haskell (GHC 7.10.3) (judge verdict: Accepted)

import Control.Arrow ((&&&))
import Data.List

isDream, isDreamer, isErase, isEraser :: String -> Bool
[(isDream, lenDream),
 (isDreamer, lenDreamer),
 (isErase, lenErase),
 (isEraser, lenEraser)] = map (isPrefixOf . reverse &&& length) ["dream", "dreamer", "erase", "eraser"]

exist :: String -> Bool
exist sna
  | null sna = True
  | isDream sna = exist $ drop lenDream sna
  | isDreamer sna = exist $ drop lenDreamer sna
  | isErase sna = exist $ drop lenErase sna
  | isEraser sna = exist $ drop lenEraser sna
  | otherwise = False

main :: IO ()
main = do
  ans <- getLine
  putStrLn $ if exist (reverse ans) then "YES" else "NO"