There is an area bounded by a fence on some flat field. The fence has
the height h and in the plane projection it has a form of a closed polygonal
line (without self-intersections), which is specified by Cartesian
coordinates (X_{i}, Y_{i}) of its N vertices. At the point with coordinates (0, 0)
a lamp stands on the field. The lamp may be located either outside or inside
the fence, but not on its side as it is shown in the following sample pictures
(parts shown in a thin line are not illuminated by the lamp):

The fence is perfectly black, i.e. it is neither reflecting, nor diffusing,
nor letting the light through. Research and experiments showed that
the following law expresses the intensity of light falling on an arbitrary
illuminated point of this fence:

I_{0}=k/r

where k is a known constant value not depending on the point in question,
r is the distance between this point and the lamp in the plane projection.
The illumination of an infinitesimal narrow vertical board with the width dl
and the height h is:

dI=I_{0} · |cos A| · dl · h

where I_{0} is the intensity of light on that board of the fence, A is the angle
in the plane projection between the normal to the side of the fence at this
point and the direction to the lamp. You are to write a program that will find
the total illumination of the fence that is defined as the sum of illuminations
of all its illuminated boards.

Input
The first line of the input file contains the numbers k, h and N, separated by
spaces. k and h are real constants. N (3<=N<=100) is the number of vertices of the
fence. Then N lines follow, every line contains two real numbers X_{i} and Y_{i},
separated by a space.

Output
Write to the output file the total illumination of the fence rounded to the
second digit after the decimal point.