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 PyPy3 (2.4.0) (judge verdict: Runtime Error)

S=list(input())
i=0
while i!=len(S):
    if S[i:i + 6] == ['e', 'r', 'a', 's', 'e', 'r']:
        i += 6
    elif S[i:i+5]==['e','r','a','s','e']:
        i+=5
    elif S[i:i+7]==['d','r','e','a','m','e','r'] and (len(S[i+7:])==7 or S[i+7]!='a'):
        i+=7
    elif S[i:i+5]==['d','r','e','a','m']:
        i+=5
    else:
        print('NO')
        exit()
print('YES')