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 {

  def main(args: Array[String]): Unit = {
    val sc = new java.util.Scanner(System.in)

    val S = sc.nextLine().reverse.toList

    def loop(S: List[Char]): Boolean =
      S match {
        case Nil => true
        case 'r' :: 'e' :: 'm' :: 'a' :: 'e' :: 'r' :: 'd' :: t => loop(t)
        case 'm' :: 'a' :: 'e' :: 'r' :: 'd' :: t => loop(t)
        case 'r' :: 'e' :: 's' :: 'a' :: 'r' :: 'e' :: t => loop(t)
        case 'e' :: 's' :: 'a' :: 'r' :: 'e' :: t => loop(t)
        case _ => false
      }

    println(if (loop(S)) "YES" else "NO")
  }

}