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: Accepted)

object Main extends App {
  val s = readLine  
  val list = Seq("dream", "dreamer", "erase", "eraser")
  
  def check(str: String): Boolean = {
    val index = list.indexWhere(str.endsWith)

    if (str.isEmpty) true
    else if (index == -1) false
    else check(str.dropRight(list(index).length))
  }
  
  val result = check(s)
  println(if (result) "YES" else "NO")
}