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=input()
b=input()
h=input()
a=int(a)
b=int(b)
h=int(h)
x=(a+b)*h
print(x*0.5)
a=input()
b=input()
h=input()
a=int(a)
b=int(b)
h=int(h)
x=(a+b)*h
print(x//2)