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;

my $s = get_array_from_stdin();

while($s) {
  if ($s eq "") {
    print "YES\n";
    exit;
  }

  if ($s =~ s/^eraser?//) {
    redo;
  }

  if ($s =~ /^dream/) {
    if ($s =~ /^dreamer/) {
      if ($s =~ s/^dreameraser?//) {
      } else {
        $s =~ s/^dreamer//;
      }
      redo;
    } else {
      $s =~ s/^dream//;
      redo;
    }
  }

  print "NO\n";
  exit;
}

### common sub routine ###

sub get_array_from_stdin {
  my $input = <STDIN>;
  chomp($input);
  if (wantarray) {
    return split /\s+/, $input;
  } else {
    return $input;
  }
}