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 Control.Monad
import Data.Maybe (fromJust)
import Data.List
import Data.Char

isDayDream :: String -> Bool
isDayDream "" = True
isDayDream s
    | (isPrefixOf "maerd" s) = isDayDream (drop 5 s)
    | (isPrefixOf "remaerd" s) = isDayDream (drop 7 s)
    | (isPrefixOf "esare" s) = isDayDream (drop 5 s)
    | (isPrefixOf "resare" s) = isDayDream (drop 6 s)
    | otherwise =  False

toYesNo :: Bool -> String
toYesNo True = "YES"
toYesNo _ = "NO"

solve :: String -> String
solve = toYesNo . isDayDream . reverse

main :: IO ()
main = do
    s <- getLine
    putStrLn $ solve s