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: Memory Limit Exceeded)

import scala.io.StdIn._

trait Solver extends App {
  implicit class Pipe[T](x: T) {
    def |>[U](f: T => U) = f(x)
  }

  class Prefix(prefix: String) {
    def unapply(s: String) = {
      if(s.startsWith(prefix)) Some(s.stripPrefix(prefix))
      else None
    }
  }

  val dream = new Prefix("dream".reverse)
  val dreamer = new Prefix("dreamer".reverse)
  val erase = new Prefix("erase".reverse)
  val eraser = new Prefix("eraser".reverse)

  def solve(s: String): Boolean = s match {
    case "" => true
    case dream(tail)   => solve(tail)
    case dreamer(tail) => solve(tail)
    case erase(tail)   => solve(tail)
    case eraser(tail)  => solve(tail)
    case _ => false
  }
}

object Main extends Solver {
  val s = readLine().reverse
  solve(s) match {
    case true => println("YES")
    case false => println("NO")
  }
}