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())
h =int(input())
print((a+b) * h * 0.5)
a =int(input())
b =int(input())
h =int(input())
print(int((a+b) * h * 0.5))