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)

s = gets.chomp
num = 0

while num <= s.size
  num2 = num
  if s[num..num+4] == 'dream'
    if s[num..num+6] == 'dreamer'
      if s[num+5..num+9] == 'erase'
        num = num - 2
      end
      num += 2
    end
    num += 5
  end
  if s[num..num+4] == 'erase'
    if s[num..num+5] == 'eraser'
      num += 1
    end
    num += 5
  end
  if num == num2
    break
  end
end

if num == s.size
  puts 'YES'
else
  puts 'NO'
end