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.util.control.Breaks

object Main{
  def main(args: Array[String]) {
    val sc = new java.util.Scanner(System.in)
    var s = sc.next

    val b = new Breaks
    b.breakable { while (s.size > 0) {
      if (s.size < 5)
        b.break
      val substr = s.take(5)
      if (substr == "erase" || substr == "dream") {
        s = s.drop(5)
        if (s.size >0 && s.head == 'r')
          s = s.drop(1)
      }
    } }
    if (s.size == 0)
      println("YES")
    else
      println("NO")
  }
}