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: Runtime Error)

object Main extends App {
  import scala.util.parsing.combinator._

  val s = scala.io.StdIn.readLine
  println(if (S(s.reverse)) "YES" else "NO")

  object S extends S {
    def apply(t: String) = parseAll(s, t) match {
      case Success(res, in) => true
      case _ => false
    }
  }
  class S private extends RegexParsers {
    def s = "(maerd|remaerd|esare|resare)+".r
  }
}