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 input = read()
        println(daydream(input))
    }

    enum class Choices { dream, dreamer, erase, eraser }

    fun read(): String {
        return readLine()!!
    }

    fun daydream(input: String): String {
        val reversed = input.reversed()
        val reversedChoices = Choices.values().map { it.name.reversed() }

        tailrec fun erasing(str: String): Boolean {
            if (str.isEmpty()) return true
            val found = reversedChoices.find { it.substring(0, 3) == str.substring(0, 3) }
            if (found == null || str.length < found.length || str.substring(0, found.length) != found)
                return false
            else
                return erasing(str.drop(found.length))
        }

        return if (erasing(reversed)) "YES" else "NO"
    }