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 <iostream>
#include <cstring>
#include <iomanip>

using namespace std;

class Point {
public:
	double x;
	double y;
};

const double esp = 1e-10;


double Cross(Point p0, Point p1, Point p2) {
	return (p1.x - p0.x) * (p2.y - p0.y) - (p2.x - p0.x) * (p1.y - p0.y);
}

int main(void) {
	int n, i;
	double sum;
	Point pointSet[21];
	char c;

	n = 0;
	while (cin >> pointSet[n].x >> c >> pointSet[n].y) {
		n++;
	}

	sum = 0;
	for (i = 1; i < n-1; i++) {
		sum += Cross(pointSet[0], pointSet[i], pointSet[i + 1]);
	}

	cout << fixed << setprecision(6) << sum / 2 << endl;

	return 0;
}