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 <iomanip>
#include <vector>
#include <utility>
#include <cmath>

using namespace std;

typedef pair<double, double> point;

double area(point A, point B, point C)
{
	double x1 = B.first  - A.first;
	double x2 = C.first  - A.first;
	double y1 = B.second - A.second;
	double y2 = C.second - A.second;
	return 0.5 * abs(x1*y2 - x2*y1);
}

int main()
{
	vector<point> coordinate;
	double x, y;
	char dummy;
	while ( cin >> x >> dummy >> y ) coordinate.push_back( make_pair(x, y) );
	
	double area_of_polygon = 0.0;
	for (vector<point>::iterator it = coordinate.begin()+1; it != coordinate.end()-1; it++) {
		area_of_polygon += area(coordinate.at(0), *it, *(it+1));
	}
	cout << fixed << setprecision(6) << area_of_polygon << endl;
	
	return 0;
}