output_description: Print the area of the triangle ABC.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      |AB| |BC| |CA|
attempt: def decrease_height_by_one(hs):
      highest_indexes = [i for i, h in enumerate(hs) if h == max(hs)]
      is_indexes_discontinuous = (
          i1 + 1 < i2 for i1, i2 in zip(highest_indexes, highest_indexes[1:])
      )
      for index in highest_indexes:
          hs[index] -= 1
      return 1 + sum(is_indexes_discontinuous)
  
  
  input()
  hs = list(map(int, input().split()))
  
  n = 0
  while max(hs):
      n += decrease_height_by_one(hs)
  print(n)
  
problem_description: Statement
  
  There is a right triangle ABC with ∠ABC=90°.
  
  Given the lengths of the three sides, |AB|,|BC| and |CA|, find the area of the
  right triangle ABC.
  
  It is guaranteed that the area of the triangle ABC is an integer.
samples: [{"input": "3 4 5", "output": "6\n    \n\n![tri](https://img.atcoder.jp/ghi/44c1d4cbdf4677ce3b08ca70b5ce98ea.png)\n\nThis triangle has an area of 6.\n\n* * *"}, {"input": "5 12 13", "output": "30\n    \n\nThis triangle has an area of 30.\n\n* * *"}, {"input": "45 28 53", "output": "630\n    \n\nThis triangle has an area of 630."}]