A bakery prepares a certain number of cookies each day. On Monday, they prepared 120 cookies, on Tuesday they prepared 180 cookies, and on Wednesday they prepared 240 cookies. The bakery wants to package the cookies in boxes such that each box contains the same number of cookies and there are no cookies left over. What is the greatest number of cookies that can be put in each box? Let's think step by step and output the final answer within \boxed{}.
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