a = list(map(float, input().split()))
x1 = a[0]
y1 = a[1]
x2 = a[2]
y2 = a[3]
x3 = a[4]
y3 = a[5]



class Vector:
    def __init__(self, x, y):
        self.x = x
        self.y = y
    def __mul__(left,right):
        return (left.x * right.y- left.y*right.x)

a=Vector(x2-x1,y2-y1)
b=Vector(x3-x1,y3-y1)


print(abs (a * b / 2))