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=s(sa)(sb)(sc)

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 (x1,y1) and (x2,y2) is

|PQ|=(x1x2)2+(y1y2)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