def main():
    used_words = []
    while True:
        word = input("Type 4 letter word: ")
        if len(word) == 4 and word not in used_words:
            used_words.append(word)
            print("good job, try another word")
        elif word in used_words:
            print("word already exists")
        elif len(word) != 4:
            print("word is not 4 letters long")