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: Wrong Answer)

import Data.List

main :: IO ()
main = do
    x <- getLine
    putStrLn (hantei "" x)

-- ここは他に回そうif as == bs then
hantei :: String -> String -> String
hantei as bs = if as == bs then "Yes"
    else if isSuffixOf ("eraser" ++ as) bs then hantei ("eraser" ++ as) bs
    else if isSuffixOf ("erase" ++ as) bs then hantei ("erase" ++ as) bs
    else if isSuffixOf ("dreamer" ++ as) bs then hantei ("dreamer" ++ as) bs
    else if isSuffixOf ("dream"  ++ as) bs then hantei ("dream"  ++ as) bs
    else "No"