Stream of letters - PB SoftUni

command = input()
valid_letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
is_c = False
is_o = False
is_n = False
secret = ""
secret_word = ""

while command != "End":
    current_symbol = command

    if current_symbol not in valid_letters:
        command = input()
        continue

    if current_symbol == "c":
        if not is_c:
            is_c = True
        else:
            secret += current_symbol

    elif current_symbol == "o":
        if not is_o:
            is_o = True
        else:
            secret += current_symbol
    elif current_symbol == "n":
        if not is_n:
            is_n = True
        else:
            secret += current_symbol

    if current_symbol not in ["c", "o", "n"]:
        secret += current_symbol

    secret_word = secret

    if is_c and is_o and is_n:
        print(secret_word, end=" ")
        secret = ""
        is_c = False
        is_o = False
        is_n = False

    command = input()