Problem 1 - Registration-exam-mistake!!

user = input()
len_user = len(user)
command = input().split()
new_string = user

while command[0] != "Registration":
    if command[0] == 'Letters' and command[1] == 'Lower':
        user = user.lower()
        print(user)
    elif command[0] == 'Letters' and command[1] == 'Upper':
        user = user.upper()
        print(user)
    elif command[0] == 'Reverse':
        start = int(command[1])
        end = int(command[2])
        if 0 <= start < len_user and 0 < end < len_user and start < end:
            substring = user[start:end+1][::-1]
            print(substring)
        else:
            print("Invalid indices. Start and end must be within the username length.")
    elif command[0] == 'Substring':
        if command[1] not in new_string:
            print(f"The username {user} doesn't contain {command[1]}.")
        else:
            new_string = new_string.replace(command[1], '')
            print(new_string)
    elif command[0] == 'Replace':
        new_string = user.replace(command[1], '-')
        print(new_string)
    elif command[0] == 'IsValid':
        if command[1] in user:
            print("Valid username.")
        else:
            print(f"{command[1]} must be contained in your username.")
    command = input().split()