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: Accepted)

(let* ((str (reverse (read-line))))
  (defun f (str-f)
    (if (not (string= str-f ""))
        (cond ((and (<= 6 (length str-f)) (string= (subseq str-f 0 6) "resare")) (f (subseq str-f 6)))
            ((and (<= 5 (length str-f)) (string= (subseq str-f 0 5) "esare")) (f (subseq str-f 5)))
            ((and (<= 7 (length str-f)) (string= (subseq str-f 0 7) "remaerd")) (f (subseq str-f 7)))
            ((and (<= 5 (length str-f)) (string= (subseq str-f 0 5) "maerd")) (f (subseq str-f 5)))
            (t nil))
        t))
  (if (f str) (princ "YES") (princ "NO")))