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 OCaml (4.02.3) (judge verdict: Wrong Answer)

let char_list_of_string str = 
  let rec f0 i a =
    if i<0 then a else f0 (i-1) (str.[i]::a)
	in f0 (String.length str - 1) []
let string_of_char_list ls = 
	List.fold_left (fun u v -> u ^ (String.make 1 v)) "" ls

let () =
	let s = read_line () |> char_list_of_string |> List.rev
	in let hoge a = a|>List.rev|>string_of_char_list
	in let rec f0 a = match a with
	| [] -> "Yes"
	|	p::q::r::s::t::u::v::tl when "dreamer" = hoge [p;q;r;s;t;u;v] -> f0 tl
	| p::q::r::s::t::u::tl when "eraser" = hoge [p;q;r;s;t;u] -> f0 tl
	| p::q::r::s::t::tl when let h = hoge [p;q;r;s;t] in "dream" = h || "erase" = h -> f0 tl
	| _ -> "No"
	in print_endline @@ f0 s