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 Ruby (2.3.3) (judge verdict: Accepted)

def cnt(str,word)
    return str.scan(word).length
end

s = gets.chomp

dreameraser = cnt(s,"dreameraser")
dreamerase  = cnt(s,"dreamerase" ) - dreameraser
dreamer = cnt(s,"dreamer") - ( dreameraser + dreamerase)
dream   = cnt(s,"dream")  -  ( dreameraser + dreamerase + dreamer)
eraser  = cnt(s,"eraser") - dreameraser
erase   = cnt(s,"erase")  - (dreameraser + dreamerase + eraser )

# puts [dreamer, dream, eraser, erase]
if s.size == 11 * dreameraser + 10 * dreamerase + 7 * dreamer + 5 * dream + 6 * eraser + 5 * erase
    puts "YES"
else
    puts "NO"
end