def detect_spam(subjects, spam_words):
    results = []
    for subject in subjects:
        count = 0
        subject_lower = subject.lower()
        for word in spam_words:
            if word.lower() in subject_lower:
                count += 1
                if count >= 2:
                    results.append("spam")
                    break
        else:
            results.append("not spam")
    return results
 
# Example usage
subjects = ["free prize worth millions", "ten tips for a carefree lifestyle"]
spam_words = ["free", "prize"]
results = detect_spam(subjects, spam_words)
print(results)  # Output: ['spam'

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