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: Runtime Error)

s = STDIN.gets.strip;
i = s.length;

dream = "dream"
dreamer = "dreamer"
erase = "erase"
eraser = "eraser"

while i > 0
  if i < 5 {
    puts "No"
    exit
  }
  slice = s[i-5...i]
  if slice == dream || slice == erase
    i = i - 5
    next
  end

  slice = s[i-6..i]
  if slice == eraser
    i = i - 6
    next;
  end

  slice = s[i-7..i];
  if slice == dreamer
    i = i - 7
    next;
  end

  puts "NO"
  exit
end

puts "Yes"