def helper(words: Set[str], chain: str, length: int, result: Set[str]):

    chain = chain.lstrip("-")

    if len(chain.split("-")) == length:
        result.add(chain)
        return result

    for word in words:

        if chain == "":
            helper(words, chain + "-" + word, length, result)
            continue

        if word not in chain.split("-"):
            if chain.split("-")[-1][-1] == word[0]:
                helper(words, chain + "-" + word, length, result)

    if len(chain.split("-")) == length:
        result.add(chain)

    return result


def word_chain(words: Set[str], length: int) -> Set[str]:
    return helper(words, "", length, set())