Problem 2 - 2.1.

def if_index_valid(index,string):
    if 0 <= index < len(string):
        return True
    return False


username = input()
data = input()
while not data == "Sign up":
    command = data.split()
    if command[0] == "Case":
        if command[1] == 'lower':
            username = username.lower()
            print(username)
        elif command[1] == 'upper':
            username = username.upper()
            print(username)
    elif command[0] == "Reverse":
        start_index, end_index = command[1:]
        start_index = int(start_index)
        end_index = int(end_index)
        if if_index_valid(start_index,username) and if_index_valid(end_index,username):
            new_Str = username[end_index:start_index-1:-1]
            print(new_Str)

    elif command[0] == "Cut":
        substring = command[1]
        if substring in username:
            username = username.replace(substring,'')
            print(username)
        else:
            print(f"The word {username} doesn't contain {substring}.")
    elif command[0] == "Replace":
        old_char = command[1]
        username = username.replace(old_char,"*")
        print(username)
    elif command[0] == "Check":
        char = command[1]
        if char in username:
            print("Valid")
        else:
            print(f"Your username must contain {char}.")


    data = input()