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 C++14 (Clang 3.8.0) (judge verdict: Accepted)

#include <iostream>
#include <string>
using namespace std;

string divide[4] = {"dream", "dreamer", "erase", "eraser"};
bool dp[100010];

int main() {
    string S;
    cin >> S;

    dp[0] = 1;
    for(int i = 0; i < S.size(); ++i){
        if(!dp[i])continue; // そこまでで矛盾があったらとりあえず無視
        for(string s : divide){
            if(S.substr(i, s.size()) == s){ // うまく切れたら先に進む
                dp[i + s.size()] = 1;
            }
        }
    }
    cout << (dp[S.size()] ? "YES" : "NO") << endl;
    return 0;
}