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.Collections.Generic;
using System.Linq;
using static System.Console;
using static System.Convert;
using static System.Math;

class Program
{
    static void Main(string[] args)
    {
        var str = ReadLine();
        str = string.Join("", str.Reverse());
        var p = new[] { "maerd", "remaerd", "esare", "resare" };
        var index = 0;
        while (index != str.Length)
        {
            if (str.Substring(index, 5) == p[0] ||
                str.Substring(index, 5) == p[2]) index += 5;
            else if (str.Substring(index, 6) == p[3]) index += 6;
            else if (str.Substring(index, 7) == p[1]) index += 7;
            else break;
        }
        WriteLine(index == str.Length? "YES" : "NO");
    }
}