Mainak has a convex polygon $$$\mathcal P$$$ with $$$n$$$ vertices labelled as $$$A_1, A_2, \ldots, A_n$$$ in a counter-clockwise fashion. The coordinates of the $$$i$$$-th point $$$A_i$$$ are given by $$$(x_i, y_i)$$$, where $$$x_i$$$ and $$$y_i$$$ are both integers.

Further, it is known that the interior angle at $$$A_i$$$ is either a right angle or a proper obtuse angle. Formally it is known that:

$$$90 ^ \circ \le \angle A_{i - 1}A_{i}A_{i + 1} \lt 180 ^ \circ$$$, $$$\forall i \in \{1, 2, \ldots, n\}$$$ where we conventionally consider $$$A_0 = A_n$$$ and $$$A_{n + 1} = A_1$$$.

Mainak's friend insisted that all points $$$Q$$$ such that there exists a chord of the polygon $$$\mathcal P$$$ passing through $$$Q$$$ with length not exceeding $$$1$$$, must be coloured $$$\color{red}{\text{red}}$$$.

Mainak wants you to find the area of the coloured region formed by the $$$\color{red}{\text{red}}$$$ points.

Formally, determine the area of the region $$$\mathcal S = \{Q \in \mathcal{P}$$$ | $$$Q \text{ is coloured } \color{red}{\text{red}}\}$$$.

Recall that a chord of a polygon is a line segment between two points lying on the boundary (i.e. vertices or points on edges) of the polygon.

Input

The first line contains an integer $$$n$$$ ($$$4 \le n \le 5000$$$) — the number of vertices of a polygon $$$\mathcal P$$$.

The $$$i$$$-th line of the next $$$n$$$ lines contain two integers $$$x_i$$$ and $$$y_i$$$ ($$$-10^9 \le x_i, y_i \le 10^9$$$) — the coordinates of $$$A_i$$$.

Additional constraint on the input: The vertices form a convex polygon and are listed in counter-clockwise order. It is also guaranteed that all interior angles are in the range $$$[90^\circ ; 180^\circ )$$$.

Output

Print the area of the region coloured in $$$\color{red}{\text{red}}$$$.

Your answer is considered correct if its absolute or relative error does not exceed $$$10^{-4}$$$.

Formally, let your answer be $$$a$$$, and the jury's answer be $$$b$$$. Your answer is accepted if and only if $$$\frac{|a - b|}{\max{(1, |b|)}} \le 10^{-4}$$$.

Note

In the first example, the polygon $$$\mathcal P$$$ can be visualised on the Cartesian Plane as:

$\text{[math]}$

Mainak and the Bleeding Polygon

Examples