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: Accepted)

using System;
using System.Text;

    class Program
    {        static void Main(string[] args)
        {
            var S = Console.ReadLine();
            var tmp = new StringBuilder();
            var maerd = new StringBuilder("maerd");
            var remaerd = new StringBuilder("remaerd");
            var esare = new StringBuilder("esare");
            var resare = new StringBuilder("resare");
            for (var i = S.Length-1;0<=i;i--)
            {
                tmp.Append(S[i]);
                if (tmp.Length < 5) continue;
                if (tmp.Equals(maerd)) tmp.Clear(); 
                if (tmp.Equals(remaerd)) tmp.Clear(); 
                if (tmp.Equals(esare)) tmp.Clear(); 
                if (tmp.Equals(resare)) tmp.Clear(); 
            }
            if (tmp.Length!=0)
            {
                Console.WriteLine("NO");
                return;
            }
            Console.WriteLine("YES");
        }
    }