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"
)

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Scan()
	s := sc.Text()
	if eraser(s, 0) {
		fmt.Println("YES")
		return
	}
	fmt.Println("NO")
}

func eraser(s string, i int) bool {
	if i == len(s) {
		return true
	}
	switch s[i] {
	case 'd':
		return eraseDream(s, i)
	case 'e':
		return eraseErase(s, i)
	default:
		return false
	}
	return false
}

func eraseDream(s string, i int) bool {
	i5 := i + 5
	if i5 < len(s) {
		i7 := i + 7
		if i7 < len(s) {
			if s[i7] == 'a' {
				return eraseErase(s, i5)
			}
			if s[i:i7] == "dreamer" {
				return eraser(s, i7)
			}
			return s[i:i5] == "dream" && eraser(s, i5)
		}
	}
	return i5 == len(s) && s[i:i5] == "dream"
}

func eraseErase(s string, i int) bool {
	i5 := i + 5
	if i5 < len(s) {
		if s[i5] == 'r' {
			if i5+1 < len(s) {
				return s[i:i5+1] == "eraser" && eraser(s, i5+1)
			}
			return i5+1 == len(s) && s[i:i5+1] == "eraser"
		}
		return s[i:i5] == "erase" && eraser(s, i5)
	}
	return i5 == len(s) && s[i:i5] == "erase"
}