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: Time Limit Exceeded)

import scala.io.StdIn._
import java.util.regex.Pattern
object Main extends App {
  val pattern = Pattern.compile("(dream|dreamer|erase|eraser)$")

  @scala.annotation.tailrec
  def removeTail(str: String): String = {
    val newStr = pattern.matcher(str).replaceFirst("")
    if (str == newStr) str else (removeTail(newStr))
  }
  println(if (removeTail(readLine) == "") "YES" else "NO")
}