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 Kotlin (1.0.0) (judge verdict: Accepted)

fun main(args: Array<String>) {
  val s = readLine()!!
  var i = s.length - 1
  while (i > 0) {
    if (i - 4 >= 0 && s.substring(i - 4..i) == "dream") {
      i -= 5
    } else if (i - 6 >= 0 && s.substring(i - 6..i) == "dreamer") {
      i -= 7
    } else if (i - 4 >= 0 && s.substring(i - 4..i) == "erase") {
      i -= 5
    } else if (i - 5 >= 0 && s.substring(i - 5..i) == "eraser") {
      i -= 6
    } else {
      println("NO")
      return
    }
  }
  println("YES")
}