Problem: Write a program that reads the coordinates of the vertices of a convex n-sided polygon (a polygon whose internal angles are less than 180 degrees, that is, a polygon that is not dented) and outputs its area. The vertices are named Vertex 1, Vertex 2, Vertex 3, ... Vertex n according to the order of edge connections.

However, n is 3 or more and 20 or less. You can also use the following formula to find the area S from the lengths a, b, and c of the three sides of the triangle.

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input

The input is given in the following format:


x1, y1
x2, y2
::
xn, yn


xi and yi are real numbers that represent the x and y coordinates of vertex i, respectively.

output

Outputs the area S (real number) on one line. The output can contain an error of 0.000001 or less.

Example

Input

0.0,0.0
0.0,1.0
1.0,1.0
2.0,0.0
1.0,-1.0


Output

2.500000

Solution (in CPP):

Solution:
#include <cmath>
#include <iostream>

using namespace std;

double Length(double x1, double y1, double x2, double y2)
{
	return sqrt(pow(x2 - x1, 2) + pow(y2 - y1, 2));
}

double Triangle_Area(double a, double b, double c)
{
	double z = (a + b + c) / 2.0;

	return sqrt(z * (z - a) * (z - b) * (z - c));
}

int main()
{
	double x[20], y[20], a, b, c, S = 0.0; int C = 0; char ch;

	while (cin >> x[C] >> ch >> y[C])
	{
		C++;
	}

	for (int i = 1; i < (C - 1); i++)
	{
		a = Length(x[0]    , y[0]    , x[i]    , y[i]    );
		b = Length(x[i]    , y[i]    , x[i + 1], y[i + 1]);
		c = Length(x[i + 1], y[i + 1], x[0]    , y[0]    );

		S += Triangle_Area(a, b, c);
	}

	cout << S << endl;

	return 0;
}