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 C# (Mono 4.6.2.0) (judge verdict: Runtime Error)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace AtCoder.Abc
{
    class Abc_049_C
    {
        // https://atcoder.jp/contests/abc049/tasks/arc065_a
        public static void Main(string[] args)
        {
            var sw = new System.IO.StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
            Console.SetOut(sw);

            string[] divide = new string[4]{ "dream", "dreamer", "erase", "eraser" };

            // 文字列の入力
            string s = Console.ReadLine();
            s = new string(s.Reverse().ToArray());
            string result = "NO";
            bool can = true;
            for (int i = 0; i < s.Length; i++)
            {
                bool can2 = false;
                for (int j = 0; j < 4; i++)
                {
                    string d = divide[j];
                    if (s.Substring(i, d.Length) == d)
                    {
                        can2 = true;
                        i += d.Length;
                    }
                }
                if (!can2)
                {
                    can = false;
                    break;
                }
            }

            if (can) result = "YES";
            Console.WriteLine(result);

            Console.Out.Flush();
        }
    }
}