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 Scala (2.11.7) (judge verdict: Wrong Answer)

import scala.io.StdIn
object Main extends App {
  def f(s: List[Char]): Boolean = {
    s match {
      case List('m','a','e','r','d', x @ _*) => f(x.toList)
      case List('r','e','m','a','e','r','d',x @ _*) => f(x.toList)
      case List('e','s','a','r','e',x @ _*) => f(x.toList)
      case List('r','e','s','a','r','e',x @ _*) => f(x.toList)
      case List() => true
      case _ => false
    }
  }
  val S = StdIn.readLine()
  if (f(S.toList)) println("YES") else println("NO")
}