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)

object Main extends App {

  def partAll(s: String, es: List[String]): Boolean = {
    if (s.length == 0) true
    else {
      es.find(e => {
        if(s.slice(0, e.length) == e)
          partAll(s.drop(e.length), es)
        else
          false
      }) match {
        case None => false
        case Some(_) => true
      }
    }
  }

  val input: String = scala.io.StdIn.readLine // S

  val es: List[String] = List("dream", "dreamer", "erase", "eraser")

  partAll(input, es) match {
    case false => println("NO")
    case true  => println("YES")
  }
}