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 Ruby (2.3.3) (judge verdict: Wrong Answer)

# Here your code !
n = gets.chomp
len = n.length
i = 0
flag = 0
if(n[0..(0+6)] == "erdream" or n[i..(i+7)] == "ereraser" or n[i..(i+6)] == "ererase")
    puts "NO"
    exit
end
while(i < len)
    if(n[i..(i+4)] == "dream")
        i+=5
        next
    elsif(n[i..(i+3)] == "eras")
        i+=4
        next
    elsif(n[i..(i+4)] == "erase")
        i+=5
        next
    elsif(n[i..(i+6)] == "erdream")
        i+=7
        next
    elsif(n[i..(i+6)] == "ererse")
        i+=7
        next
    elsif(n[i..(i+5)] == "ereras")
        i+=6
        next
    elsif(n[i..(i+6)] == "ererase")
        i+=7
        flag = 1
        next
    else
        next if(len - i == 2 and n[i..(i+1)]== "er" and flag == 0) 
        puts "NO"
        exit
    end
    flag = 0
end
puts "YES"