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 "fmt"

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

	ss := map[string]bool{"maerd": true, "remaerd": true, "esare": true, "resare": true}

	t := ""
	for i := 0; i < len(s); i++ {
		t += string(s[i])
		if ss[t] {
			t = ""
		}
		if 7 < len(t) {
			break
		}
	}

	if t == "" {
		fmt.Println("YES")
	} else {
		fmt.Println("NO")
	}

}

func reverse(s string) string {
	runes := []rune(s)
	for i, j := 0, len(runes)-1; i < j; i, j = i+1, j-1 {
		runes[i], runes[j] = runes[j], runes[i]
	}
	return string(runes)
}