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 Data.Bool
import Data.Char
import Data.List

main = interact $ bool "NO" "YES" . sol . filter isLower

sol s
  | null s                = True
  | ts!!0 `isSuffixOf` s  = sol (take (length s-5) s)
  | ts!!1 `isSuffixOf` s  = sol (take (length s-7) s)
  | ts!!2 `isSuffixOf` s  = sol (take (length s-5) s)
  | ts!!3 `isSuffixOf` s  = sol (take (length s-6) s)
  | otherwise             = False

ts = ["dream","dreamer","erase","eraser"]