输入：head = [2,1,5]
let bufferedEnd = 0;
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因此，人们选择在制度之外经营，并不是道德堕落，而是制度排斥。他们在非正式网络中完成占地、交易与仲裁。这些规则未必高效，但至少可行。然而，这套体系无法标准化，无法跨区域使用，也无法被金融系统识别，一个在贫民窟有效的“地契”，在银行依然一文不值。
But in the worst-case scenario, the Deorbit Vehicle won’t be ready. Without it, a protocol agreed on in 2024, which relies on the Russian Progress spacecraft, could come into play. There will be vexing trade-offs to consider. Allowing the ISS to descend toward Earth on its own saves gas, which the ISS will need when it’s finally time to eject into the atmosphere and ensure a burial at sea. But a slow descent jeopardizes the machinery needed to maintain remote control.