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: Memory Limit Exceeded)

use strict;

my $s = get_array_from_stdin();

if (check($s)) {
  print "YES\n";
} else {
  print "NO\n";
}

# return 1 if true;
sub check {
  my $s = shift;

  return 1 if $s eq "dream";
  return 1 if $s eq "dreamer";
  return 1 if $s eq "erase";
  return 1 if $s eq "eraser";

  if ($s =~ /^e/) {
    if ($s =~ /^eraser?(.+)/) {
      return check($1);
    }
    return 0;
  }

  unless ($s =~ /^d/) {
    return 0;
  }

  # start with "d"
  return 0 unless $s =~ /^dream/;

  # start with "dream"

  # まず dream でとってみる
  $s =~ /^dream(.+)/;
  if (check($1)) {
    return 1;
  }

  # dream では取れなかったので、dreamer で取れるか試す
  if ($s =~ /^dreamer(.+)/) {
    return check($1);
  }

  return 0;
}

### common sub routine ###

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