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.next

    def rec(s: String): String = {
      if (s.isEmpty) {
        println("YES")
        sys.exit()
      }
      if (s.startsWith("dream")) {
        if (s.startsWith("dreameraser")) {
          rec(s.replaceFirst("dreameraser", ""))
        } else if (s.startsWith("dreamerase")) {
          rec(s.replaceFirst("dreamerase", ""))
        } else if (s.startsWith("dreamer")) {
          rec(s.replaceFirst("dreamer", ""))
        } else {
          rec(s.replaceFirst("dream", ""))
        }
      } else if (s.startsWith("erase")) {
        if (s.startsWith("eraser")) {
          rec(s.replaceFirst("eraser", ""))
        } else {
          rec(s.replaceFirst("erase", ""))
        }
      } else {
        println("NO")
        sys.exit()
      }
    }

    rec(S)
  }
}