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 Go (1.6) (judge verdict: Accepted)

package main

import (
	"bufio"
	"fmt"
	"os"
	"strings"
)

func main() {
	r := bufio.NewReaderSize(os.Stdin, 200000)
	s, _, _ := r.ReadLine()

	if daydream(string(s)) {
		fmt.Println("YES")
	} else {
		fmt.Println("NO")
	}
}

func daydream(s string) bool {
	if s == "" {
		return true
	}

	if strings.HasPrefix(s, "dreamer") {
		return daydream(s[7:]) || daydream(s[5:])
	} else if strings.HasPrefix(s, "dream") {
		return daydream(s[5:])
	} else if strings.HasPrefix(s, "eraser") {
		return daydream(s[6:])
	} else if strings.HasPrefix(s, "erase") {
		return daydream(s[5:])
	}

	return false
}