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 Data.Bool
import Data.List

main = getLine >>= putStrLn . bool "NO" "YES" . dd . Just . reverse

dd Nothing = False
dd (Just "") = True
dd (Just s@('m':_)) = dd (stripPrefix "maerd" s)
dd (Just s@('r':'e':'m':_)) = dd (stripPrefix "remaerd" s)
dd (Just s@('e':_)) = dd (stripPrefix "esare" s)
dd (Just s@('r':'e':'s':_)) = dd (stripPrefix "resare" s)
dd _ = False