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: Wrong Answer)

import Data.List
import Control.Monad
import Control.Applicative

data YesNo = Yes | No deriving(Show)


solver :: String  -> YesNo
solver s
    | null s = Yes
    | isPrefixOf "remaerd" s = solver $ drop 7 s
    | isPrefixOf "maerd"   s = solver $ drop 5 s
    | isPrefixOf "resare"  s = solver $ drop 6 s
    | isPrefixOf "esare"   s = solver $ drop 5 s
    | otherwise      = No

main :: IO ()
main = getLine >>= (print . solver . reverse)