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 ((s (nreverse (read-line))))
  (labels ((f (str)
             (cond ((string= "" str) t)
                   ((and (>= (length str) 7)
                         (string= "remaerd" str :end2 7)) (f (subseq str 7)))
                   ((and (>= (length str) 6) 
                         (string= "resare" str :end2 6)) (f (subseq str 6)))
                   ((and (>= (length str) 5)
                         (string= "maerd" str :end2 5)) (f (subseq str 5)))
                   ((and (>= (length str) 5)
                         (string= "esare" str :end2 5)) (f (subseq str 5)))
                   (t nil))))
    (format t "~A~%" (if (f s) 'yes 'no))))