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.List

test [] = "YES"
test str@('m':sx) = if isPrefixOf "maerd" str
                    then test $ drop 5 str
                    else "NO"
test str@('r':sx) = if isPrefixOf "remaerd" str
                    then test $ drop 7 str
                    else if isPrefixOf "resare" str
                         then test $ drop 6 str
                         else "NO"
test str@('e':sx) = if isPrefixOf "esare" str
                    then test $ drop 5 str
                    else "NO"
test _ = "NO"

main = do
  l <- getLine
  let o = test $ reverse l
  putStrLn o