def measure(array):
    spaces = len(array)
    left = array.copy()
    right = array.copy()
    max_left = max_right = 0

    for i in range(spaces):
        left[i] = max_left = max(left[i], max_left)
        right[spaces-i-1] = max_right = max(right[spaces-i-1], max_right)

    return sum([min(l, r) - h for h, l, r in zip(array, left, right)])

print(measure([6,0,6,1,5]))