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 Rust (1.42.0) (judge verdict: Accepted)

use proconio::input;
use proconio::marker::Chars;

fn main() {
    input! {
        s: Chars,
    }

    let mut index = 0;

    while index < s.len() {
        if index + 4 < s.len() {
            let substring = s.iter().rev().skip(index).take(5).collect::<String>();
            match substring.as_str() {
                "maerd" | "esare" => {
                    index += 5;
                    continue;
                }
                _ => {},
            }

        }
        if index + 5 < s.len() {
            let substring = s.iter().rev().skip(index).take(6).collect::<String>();
            match substring.as_str() {
                "resare" => {
                    index += 6;
                    continue;
                }
                _ => {},
            }
        }
        if index + 6 < s.len() {
            let substring = s.iter().rev().skip(index).take(7).collect::<String>();
            match substring.as_str() {
                "remaerd" => {
                    index += 7;
                    continue;
                }
                _ => {},
            }
        }
        println!("NO");
        return;
    }

    if index == s.len() {
        println!("YES");
    } else {
        println!("NO");
    }
}