Score : $100$ points
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.
The input is given from Standard Input in the following format:
$a$ $b$ $h$
Print the area of the given trapezoid. It is guaranteed that the area is an integer.
3 4 2
When the lengths of the upper base, lower base, and height are $3$, $4$, and $2$, respectively, the area of the trapezoid is $(3+4)×2/2 = 7$.
4 4 4
In this case, a parallelogram is given, which is also a trapezoid.