Building Boxes LeetCode solution in Python

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# Runtime: 68 ms (Top 24.24%) | Memory: 13.9 MB (Top 54.55%)
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class Solution:
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    def minimumBoxes(self, n: int) -> int:
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        r = 0
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        while (n_upper := r * (r + 1) * (r + 2) // 6) < n:
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            r += 1
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        m = r * (r + 1) // 2
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        for i in range(r, 0, -1):
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            if (n_upper - i) < n:
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                break
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            n_upper -= i
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            m -= 1
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        return m