You are given a trapezoid. The lengths of its upper base, lower base, and height are a, b, and h, respectively.    An example of a trapezoid  Find the area of this trapezoid.
a =  int(input())
b =  int(input())
c =  int(input())
print((a+b) * c / 2)
a =  int(input())
b =  int(input())
c =  int(input())
print(int((a+b) * c / 2))