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