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: Time Limit Exceeded)

import qualified Data.ByteString.Char8 as BC

main = do
  s <- BC.unpack . BC.reverse <$> BC.getLine
  if solve s then putStrLn "YES"
             else putStrLn "NO"

solve :: String -> Bool
solve s
  | length s >= 7 && (take 7 s) == "remaerd" = solve $ drop 7 s
  | length s >= 6 && (take 6 s) == "resare" = solve $ drop 6 s
  | length s >= 5 && (take 5 s) == "maerd" = solve $ drop 5 s
  | length s >= 5 && (take 5 s) == "esare" = solve $ drop 5 s
  | otherwise = length s == 0