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: Memory Limit Exceeded)

private fun readStrings() = readLine()!!.split(" ")
private fun readInts() = readStrings().map { it.toInt() }

private fun String.dropIfStartsWith(s: String) = if (startsWith(s)) drop(s.length) else null

private fun String.searchSeparationPath(targets: List<String>): Unit? =
        if (isEmpty()) Unit
        else targets.mapNotNull {
            dropIfStartsWith(it)?.searchSeparationPath(targets)
        }.firstOrNull()

fun main(args: Array<String>) {
    val S = readLine()!!
    val targets = listOf("dreamer", "dream", "eraser", "erase")
    println(if(S.searchSeparationPath(targets) != null) "YES" else "NO")
}