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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.*;

public class Main {    
    public static void main(String[] args){

       Scanner sc = new Scanner(System.in);
                
        String S = sc.next();
		int N = S.length();
	
		int current = N;
	
		while(current > 0){
			if(current >= 7){
				String sub = S.substring(current-7, current);
				if(sub.equals("dreamer")){
					current -= 7;
					continue;
				}
			}
			
			if(current >= 6){
				String sub = S.substring(current-6, current);
				if(sub.equals("eraser")){
					current -= 6;
					continue;
				}
			}
			
			if(current >= 5){
				String sub = S.substring(current-5, current);
				if(sub.equals("dream") || sub.equals("erase")){
					current -= 5;
					continue;
				}
			}
			
			System.out.println("NO");
                        return;
		}
		
		System.out.println("YES");      
                
      
  }                                      
}