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 (2.13.1) (judge verdict: Accepted)

object Main extends App {
  val sc = new java.util.Scanner(System.in)
  val s = sc.next()

  def solve(s: String): Boolean = {
    if (s.isEmpty) {
      true
    } else if (s.endsWith("dream")) {
      solve(s.dropRight(5))
    } else if (s.endsWith("dreamer")) {
      solve(s.dropRight(7))
    } else if (s.endsWith("erase")) {
      solve(s.dropRight(5))
    } else if (s.endsWith("eraser")) {
      solve(s.dropRight(6))
    } else {
      false
    }
  }

  if (solve(s)) {
    println("YES")
  } else {
    println("NO")
  }
}