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"
	"regexp"
	"strconv"
)

func solve() {
	s := next()
	// phrases := []string{"dream", "dreamer", "erase", "eraser"}
	r := regexp.MustCompile(`^(dream(er)?|eraser?)*$`)

	if r.MatchString(s) {
		println("YES")
	} else {
		println("NO")
	}
	return
}

func main() {
	defer out.Flush()
	in.Buffer(make([]byte, scBufSize), scBufSize)
	in.Split(bufio.ScanWords)

	solve()
}

// --- template ---

const scBufSize = 1e6

var (
	in  = bufio.NewScanner(os.Stdin)
	out = bufio.NewWriter(os.Stdout)
)

func println(a ...interface{}) {
	fmt.Fprintln(out, a...)
}

func printf(format string, a ...interface{}) {
	fmt.Fprintf(out, format, a...)
}

func next() string {
	in.Scan()
	return in.Text()
}

func nextInt() int {
	s := next()
	i, e := strconv.Atoi(s)
	if e != nil {
		fmt.Println(e)
	}
	return i
}

func nextInts(n int) []int {
	res := make([]int, n)
	for i := 0; i < n; i++ {
		res[i] = nextInt()
	}
	return res
}

func unique(list []int) []int {
	m := make(map[int]bool)
	uniq := make([]int, 0)
	for _, e := range list {
		if !m[e] {
			m[e] = true
			uniq = append(uniq, e)
		}
	}
	return uniq
}