def f1():
a = int(input())
b = int(input())
return a % b == 0
def f2():
a = float(input())
b = float(input())
c = float(input())
return a + b > c or a + c > b or b + c > a
def f3():
a = float(input())
b = float(input())
h = float(input())
return (a + b) * h / 2