input: def max_revenue(prices: List[int]) -> int:
      """Calculate the maximum revenue that can be obtained from a given list of prices.
      The function works by calculating the difference between consecutive prices, and then
      finding the maximum sum of any contiguous subarray of these differences.
      >>> max_revenue([10, 7, 5, 8, 11, 9])
      6
      """
output:     differences = [prices[i+1] - prices[i] for i in range(len(prices) - 1)]
      max_sum = current_sum = 0
      for diff in differences:
          current_sum = max(diff, current_sum + diff)
          max_sum = max(max_sum, current_sum)
      return max_sum