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 check(s)
  t = ['dream','dreamer','erase','eraser'].map(&:reverse)
  while s.length > 0
    if s.length >= 5 && t.include?(s.reverse[0..4])
      s = s[0..-6]
    elsif s.length >= 6 && t.include?(s.reverse[0..5])
      s = s[0..-7]
    elsif s.length >= 7 && t.include?(s.reverse[0..6])
      s = s[0..-8]
    else
      return "NO"
    end
  end
  "YES"
end

s = gets.chomp
puts check(s)