a=int(eval(input()))

b=int(eval(input()))

h=int(eval(input()))

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

b = int(eval(input()))

h = int(eval(input()))

print(((a + b) * h // 2))

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

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

-print((int((a + b) * h / 2))) +print(((a + b) * h // 2))