Stream of letters

secret_message = ''
word = ''
interval = ''
letter_counter = 0

while True:
    letter = input()
    if letter == 'End':
        break

    if letter.isalpha():
        if letter not in interval and (letter == 'o' or letter == 'c' or letter == 'n'):
            interval += letter
            letter_counter += 1

            if letter_counter == 3:
                word += ' '
                secret_message += word
                word = ''
                interval = ''
                letter_counter = 0
        else:
            word += letter
    else:
        pass

print(secret_message)