def mostcommonword(text):
    wordcounts = {}
    words = text.lower().split()

    for word in words:
        wordcounts[word] = wordcounts.get(word, 0) + 1

    sortedwords = sorted(wordcounts.items(), key=lambda x: (-x[1], x[0]))
    return sortedwords[0][0]


text = "Apple banana apple Banana kiwi"
print(mostcommonword(text))