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 Common Lisp (SBCL 1.1.14) (judge verdict: Wrong Answer)

(let* ((str (read-line)))
  (defun eval-f (a)
    (print a)
    (if (<= (length a) (length str))
        (and (string= a (subseq str 0 (length a))) (f a))))
  (defun f (a)
    (cond ((string= a str))
          ((eval-f (concatenate 'string a "dream")))
          ((eval-f (concatenate 'string a "dreamer")))
          ((eval-f (concatenate 'string a "erase")))
          ((eval-f (concatenate 'string a "eraser")))))
  (if (f "") (princ "YES") (princ "NO")))