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: Wrong Answer)

package main

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

var sc = bufio.NewScanner(os.Stdin)

func main() {

	sc.Scan()
	S := sc.Bytes()

	for i := 0; i < len(S); {
		b, c := confirm(S[i:])
		if !b {
			fmt.Println("NO")
			return
		}

		i += c
	}

	fmt.Println("YES")

}

func confirm(b []byte) (bool, int) {
	if has(b, []byte("dream")) {
		if len(b) == 5 {
			return true, 5
		}

		if has(b[5:], []byte("d")) {
			return true, 5
		}

		if !has(b[5:], []byte("er")) {
			return false, -1
		}

		if !has(b[5:], []byte("era")) {
			return true, 7
		}
		return true, 5
	}

	if has(b, []byte("eraser")) {
		return true, 6
	}

	if has(b, []byte("erase")) {
		return true, 5
	}

	return false, -1
}

// b の先頭が t かどうか
func has(b []byte, t []byte) bool {
	if len(b) < len(t) {
		return false
	}

	for i := range t {
		if b[i] != t[i] {
			return false
		}
	}
	return true
}