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 <complex>
#include <cmath>
#include <vector>
#include <queue>

using namespace std;
typedef complex<double> com;

double tri(com a, com b) //triangle size
{
	return(conj(a)*b).imag() / 2;
}
struct cou {
	bool operator()(com a, com b) {
		return tri(a, b)<0;
	}
}; //Counterclockwise

priority_queue<com, vector<com>, cou> n; //node
double x, y, xo, yo;
double S = 0;
char s;
com a;

int main()
{
	cout.setf(ios::fixed);
	cin >> xo >> s >> yo;
	while (cin >> x >> s >> y)
	{
		n.push(com(x - xo, y - yo));
	}
	while (!n.empty())
	{
		a = n.top();
		n.pop();
		if (n.empty()) break;
		S += tri(a, n.top());
	}
	cout << setprecision(8) << S << endl;
	return 0;
}