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 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
using namespace std;

int main()
{
	bool flag = true;
	string s;
	cin >> s;
	for (int i = s.size() - 1; i >= 0; i--) {
		if (i >= 6 && s.substr(i - 6, 7) == "dreamer") {
			i -= 6;
		}
		else if (i >= 4 && s.substr(i - 4, 5) == "dream") {
			i -= 4;
		}
		else if (i >= 5 && s.substr(i - 5, 6) == "eraser") {
			i -= 5;
		}
		else if (i >= 4 && s.substr(i - 4, 5) == "erase") {
			i -= 4;
		}
		else {
			cout << "NO" << endl;
			flag = false;
			break;
		}
	}
	if (flag) {
		cout << "YES" << endl;
	}
	return 0;
}