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 (
	"fmt"
	"math"
	"regexp"
)

var S string

func main() {
	fmt.Scan(&S)
	r := regexp.MustCompile(`^(eraser|erase|dreamer|dream)`)
	if r.MatchString(S) {
		fmt.Println("YES")
	} else {
		fmt.Println("NO")
	}
}

/*  ----------------------------------------  */

func gcd(x, y uint64) uint64 {
	if x%y == 0 {
		return y
	} else {
		r := x % y
		return gcd(y, r)
	}
}

func combination(x, y int) int {
	return permutation(x, y) / permutation(y, y)
}

func permutation(x, y int) int {
	var ans int = 1
	for i := x - y; 0 < i; i-- {
		ans *= i
	}
	return ans
}

func max(x ...int) int {
	var res int = x[0]
	for i := 1; i < len(x); i++ {
		res = int(math.Max(float64(x[i]), float64(res)))
	}
	return res
}

func min(x ...int) int {
	var res int = x[0]
	for i := 1; i < len(x); i++ {
		res = int(math.Min(float64(x[i]), float64(res)))
	}
	return res
}
func pow(x, y int) int { return int(math.Pow(float64(x), float64(y))) }
func abs(x int) int    { return int(math.Abs(float64(x))) }
func floor(x int) int  { return int(math.Floor(float64(x))) }

type XY struct {
	x int
	y int
}

type SortBy [][]int

func (a SortBy) Len() int      { return len(a) }
func (a SortBy) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
func (a SortBy) Less(i, j int) bool {
	return a[i][1] < a[j][1]
}