There are several formulae for calculating the area $$o$$ of a given triangle $$ABC$$. The Greek mathematician Hero of Alexandria proved the following formula circa 60 BC:

\[o = \sqrt{s(s-a)(s-b)(s-c)}\]

Hero's formula makes it possible to determine the area of a triangle when only the lengths of the sides are known. In this formula, $$a$$, $$b$$ and $$c$$ are the lengths of the sides of the triangle and $$s$$ is the half-circumference of the triangle. Use Hero's formula to determine the area of the given triangle, bearing in mind that the Euclidean distance between two points $$P$$ and $$Q$$, with the co-ordinates ($$x_1$$,$$y_1$$) and ($$x_2$$,$$y_2$$) is

\[|PQ| = \sqrt{(x_1-x_2)^2 + (y_1-y_2)^2}\]

Input

Six lines with the co-ordinates of the vertices of the triangle $$ABC$$: line 1 contains the $$x$$-co-ordinate of the vertex $$A$$, line 2 contains the $$y$$-co-ordinate of the vertex $$A$$, …, line 6 contains the $$y$$-co-ordinate of the vertex $$C$$. All co-ordinates are given as whole numbers.

Output

The area of the triangle, as a decimal number.

Example

Input:

0
0
2
2
1
0

Output:

1.0