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: A = [int(n) for n in input().split())
  print(A[0]*A[1]/2)
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."}]