output_description: Print the maximum value in a line.
input_description: The first line contains an integer $n$. In the following $n$ lines, $R_t$ ($t
  = 0, 1, 2, ... n-1$) are given in order.
attempt: #!/usr/bin/env python
  # -*- coding: utf-8 -*-
  
  """
  input:
  6
  5
  3
  1
  3
  4
  3
  
  output:
  3
  """
  
  import sys
  
  
  def solve():
      # write your code here
      max_profit = 0
      min_stock = prices[0]
      for price in prices[1:]:
          max_profit = max(max_profit, price - min_stock)
          min_stock = min(min_stock, price)
      return max_profit if max_profit else -1
  
  
  if __name__ == "__main__":
      _input = sys.stdin.readlines()
      p_num = int(_input[0])
      prices = list(map(int, _input[1:]))
      print(solve())
  
problem_description: Maximum Profit
  
  You can obtain profits from foreign exchange margin transactions. For example,
  if you buy 1000 dollar at a rate of 100 yen per dollar, and sell them at a
  rate of 108 yen per dollar, you can obtain (108 - 100) × 1000 = 8000 yen.
  
  Write a program which reads values of a currency $R_t$ at a certain time $t$
  ($t = 0, 1, 2, ... n-1$), and reports the maximum value of $R_j - R_i$ where
  $j > i$ .
samples: [{"input": "6\n    5\n    3\n    1\n    3\n    4\n    3", "output": "3"}, {"input": "3\n    4\n    3\n    2", "output": "-1"}]