output_description: Print the area of the given trapezoid. It is guaranteed that the area is an
  integer.
  
  * * *
input_description: The input is given from Standard Input in the following format:
  
      
      
      a
      b
      h
attempt: a=int(input()
  b=int(input()
  h=int(input()
  print((a+b)*h//2)
problem_description: Statement
  
  You are given a trapezoid. The lengths of its upper base, lower base, and
  height are a, b, and h, respectively.
  
  ![](https://atcoder.jp/img/arc061/1158e37155d46a42e90f31566478e6da.png)
  
  An example of a trapezoid
  
  Find the area of this trapezoid.
samples: [{"input": "3\n    4\n    2", "output": "7\n    \n\nWhen the lengths of the upper base, lower base, and height are 3, 4, and 2,\nrespectively, the area of the trapezoid is (3+4)\u00d72/2 = 7.\n\n* * *"}, {"input": "4\n    4\n    4", "output": "16\n    \n\nIn this case, a parallelogram is given, which is also a trapezoid."}]