Buggy python submission (verdict: Time Limit Exceeded):
#coding:utf-8
import re

if __name__ == "__main__":
    patterns = ["dream", "dreamer", "erase" ,"eraser"]
    S = input()

    # while True:
    #     flag = False
    #     if S[-5:] == "dream":
    #         S = S[:-5]
    #         flag = True
    #     if S[-7:] == "dreamer":
    #         S = S[:-7]
    #         flag = True
    #     if S[-5:] == "erase":
    #         S = S[:-5]
    #         flag = True
    #     if S[-6:] == "eraser":
    #         S = S[:-6]
    #         flag = True
    #
    #     if flag == False:
    #         print("NO")
    #         break
    #
    #     if S == "":
    #         print("YES")
    #         break

    while True:
        flag = False
        if re.search("dream$",S):
            S = re.sub("dream$","",S)
            flag = True
        if re.search("dreamer$",S):
            S = re.sub("dreamer$","",S)
            flag = True
        if re.search("erase$",S):
            S = re.sub("erase$","",S)
            flag = True
        if re.search("eraser$",S):
            S = re.sub("eraser$","",S)
            flag = True

        if flag == False:
            print("NO")
            break

        if S == "":
            print("YES")
            break

Fixed submission:
#coding:utf-8
import re

if __name__ == "__main__":
    patterns = ["dream", "dreamer", "erase" ,"eraser"]
    S = input()

    while True:
        flag = False
        if S[-5:] == "dream":
            S = S[:-5]
            flag = True
        if S[-7:] == "dreamer":
            S = S[:-7]
            flag = True
        if S[-5:] == "erase":
            S = S[:-5]
            flag = True
        if S[-6:] == "eraser":
            S = S[:-6]
            flag = True

        if flag == False:
            print("NO")
            break

        if S == "":
            print("YES")
            break

Buggy python submission (verdict: Runtime Error):
#coding:utf-8
import re

if __name__ == "__main__":
    patterns = ["dream", "dreamer", "erase" ,"eraser"]
    S = input()

    # while True:
    #     flag = False
    #     if S[-5:] == "dream":
    #         S = S[:-5]
    #         flag = True
    #     if S[-7:] == "dreamer":
    #         S = S[:-7]
    #         flag = True
    #     if S[-5:] == "erase":
    #         S = S[:-5]
    #         flag = True
    #     if S[-6:] == "eraser":
    #         S = S[:-6]
    #         flag = True
    #
    #     if flag == False:
    #         print("NO")
    #         break
    #
    #     if S == "":
    #         print("YES")
    #         break

    while True:
        flag = False
        if re.search("dream$",S):
            S = re.sub("dream$","",S)
            flag = True
        if re.search("dreamer$",S):
            S = re.sub("dreamer$","",S)
            flag = True
        if re.search("erase$",S):
            S = re.sub("erase$","",S)
            flag = True
        if re.search("eraser$",S):
            S = r
            

Fixed submission:
#coding:utf-8
import re

if __name__ == "__main__":
    patterns = ["dream", "dreamer", "erase" ,"eraser"]
    S = input()

    while True:
        flag = False
        if S[-5:] == "dream":
            S = S[:-5]
            flag = True
        if S[-7:] == "dreamer":
            S = S[:-7]
            flag = True
        if S[-5:] == "erase":
            S = S[:-5]
            flag = True
        if S[-6:] == "eraser":
            S = S[:-6]
            flag = True

        if flag == False:
            print("NO")
            break

        if S == "":
            print("YES")
            break

Buggy python submission (verdict: Time Limit Exceeded):
#coding:utf-8
import re

if __name__ == "__main__":
    patterns = ["dream", "dreamer", "erase" ,"eraser"]
    S = input()

    end = False

    while not(end):
        flag = False
        for pattern in patterns:
            if flag == False:
                if re.search(pattern+"$",S):
                    S = re.sub(pattern+"$","",S)
                    flag = True
            elif flag == True:
                break
        else:
            if flag == False:
                print("NO")
                end = True

        if not(S):
            print("YES")
            end = True

Fixed submission:
#coding:utf-8
import re

if __name__ == "__main__":
    patterns = ["dream", "dreamer", "erase" ,"eraser"]
    S = input()

    while True:
        flag = False
        if S[-5:] == "dream":
            S = S[:-5]
            flag = True
        if S[-7:] == "dreamer":
            S = S[:-7]
            flag = True
        if S[-5:] == "erase":
            S = S[:-5]
            flag = True
        if S[-6:] == "eraser":
            S = S[:-6]
            flag = True

        if flag == False:
            print("NO")
            break

        if S == "":
            print("YES")
            break