Slowest eating speed

Banana piles must all be eaten within h hours, one pile at a time at a fixed speed. Find the smallest speed that works.

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import math
def min_speed(piles, h):
    lo, hi = 1, max(piles)
    while lo < hi:
        mid = (lo + hi) // 2
        hours = sum(math.ceil(p / mid) for p in piles)
        if hours <= h: hi = mid     # works, try slower
        else: lo = mid + 1
    return lo