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)
a = int(input())
b = int(input())
h = int(input())
print(int((a+b)*h/2))