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.
#!/usr/bin/env python3
# -*- coding: utf-8 -*-

A = int(input())
B = int(input())
H = int(input())

print((A + B) * H / 2)

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

A = int(input())
B = int(input())
H = int(input())

print(int((A + B) * H / 2))
