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 <algorithm>
#include <iostream>
#include <vector>
using namespace std;

int main() {
    string s; cin >> s;
    int n = s.length();

    vector<int> dp(n + 1, 0);
    dp[0] = 1;
    for (int i = 0; i < n; i++) if (dp[i]) {
        if (i + 5 <= n and s.substr(i, 5) == "dream")   dp[i + 5] = 1;
        if (i + 7 <= n and s.substr(i, 7) == "dreamer") dp[i + 7] = 1;
        if (i + 5 <= n and s.substr(i, 5) == "erase")   dp[i + 5] = 1;
        if (i + 6 <= n and s.substr(i, 6) == "eraser")  dp[i + 6] = 1;
    }

    puts(dp[n] ? "YES" : "NO");

    return 0;
}