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: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Text;
using System.Numerics;
using System.IO;


namespace SolutionCS
{
    class Program
    {
        static void Main(string[] args)
        {
            string s = Console.ReadLine();

            while(s.Length >= 5)
            {
                int pos = s.Length;

                string ss = s.Substring(pos - 5, 5);

                if ( ss.CompareTo("erase") == 0 ||
                    ss.CompareTo("dream") == 0 )
                {
                    s = s.Substring(0, pos - 5);
                    continue;
                }

                if (pos >= 7)
                {
                    ss = s.Substring(pos - 7, 7);
                    if (ss.CompareTo("dreamer") == 0)
                    {
                        s = s.Substring(0, pos - 7);
                        continue;
                    }
                }

                if (pos >= 6)
                {
                    ss = s.Substring(pos - 6, 6);
                    if (ss.CompareTo("eraser") == 0)
                    {
                        s = s.Substring(0, pos - 6);
                        continue;
                    }
                }


                Console.WriteLine("No");
                return;
            }

            if ( s.Length != 0)
            {
                Console.WriteLine("No");
                return;
            }

            Console.WriteLine("Yes");
        }
    }
}