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 Perl (v5.18.2) (judge verdict: Accepted)

use strict;
use warnings;

main();

sub main{
	my $input = <stdin>;
	chomp($input);

	while(1){
		my $len = length($input);
		# printf("%d : %s\n", $len, $input);

		if(rindex($input,'dreamer') == $len-7){
			$input = substr($input, 0, -7);
		}
		elsif(rindex($input,'dream') == $len-5){
			$input = substr($input, 0, -5);
		}
		elsif(rindex($input,'eraser') == $len-6){
			$input = substr($input, 0, -6);
		}
		elsif(rindex($input,'erase') == $len-5){
			$input = substr($input, 0, -5);
		}
		else{
			print "NO\n";
			return;
		}

		if(length($input) == 0){
			print "YES\n";
			return;
		}
	}
}
1;