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: import sys, re
  from collections import deque, defaultdict, Counter
  from math import ceil, sqrt, hypot, factorial, pi, sin, cos, radians
  from heapq import heappop, heappush, heapify, heappushpop
  from bisect import bisect_left, bisect_right
  from itertools import permutations, combinations, product
  from operator import itemgetter, mul
  from copy import deepcopy
  from functools import reduce, partial
  from fractions import Fraction
  from string import ascii_lowercase, ascii_uppercase, digits
  
  def input(): return sys.stdin.readline().strip()
  def INT(): return int(input())
  def MAP(): return map(int, input().split())
  def LIST(): return list(map(int, input().split()))
  sys.setrecursionlimit(10 ** 9)
  INF = float('inf')
  MOD = 10 ** 9 + 7
  
  a = INT()
  b = INT()
  h = INT()
  print(int((a+b)*h/2))import sys, re
  from collections import deque, defaultdict, Counter
  from math import ceil, sqrt, hypot, factorial, pi, sin, cos, radians
  from heapq import heappop, heappush, heapify, heappushpop
  from bisect import bisect_left, bisect_right
  from itertools import permutations, combinations, product
  from operator import itemgetter, mul
  from copy import deepcopy
  from functools import reduce, partial
  from fractions import Fraction
  from string import ascii_lowercase, ascii_uppercase, digits
  
  def input(): return sys.stdin.readline().strip()
  def INT(): return int(input())
  def MAP(): return map(int, input().split())
  def LIST(): return list(map(int, input().split()))
  sys.setrecursionlimit(10 ** 9)
  INF = float('inf')
  MOD = 10 ** 9 + 7
  
  a = INT()
  b = INT()
  h = INT()
  print(int((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."}]