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 (
	"errors"
	"fmt"
	"os"
	"strings"
)

func main() {
	var s string
	fmt.Scan(&s)

	if s[:1] != "d" && s[:1] != "e" {
		fmt.Println("NO")
		os.Exit(0)
	}

	for {
		var err error
		s, err = removeMatchedStr(s)
		if err != nil {
			fmt.Println("NO")
			os.Exit(0)
		}
		if len(s) == 0 {
			break
		}
	}
	fmt.Println("YES")
}

func removeMatchedStr(s string) (string, error) {
	if s == "dreamer" || s == "dream" || s == "eraser" || s == "erase" {
		return "", nil
	}

	if strings.HasSuffix(s, "dreamer") {
		return strings.TrimSuffix(s, "dreamer"), nil
	}

	if strings.HasSuffix(s, "dream") {
		return strings.TrimSuffix(s, "dream"), nil
	}

	if strings.HasSuffix(s, "eraser") {
		return strings.TrimSuffix(s, "eraser"), nil
	}

	if strings.HasSuffix(s, "erase") {
		return strings.TrimSuffix(s, "erase"), nil
	}

	return "", errors.New("string is not found")
}