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 <cmath>
using namespace std;

double S(double a, double b, double c){
	double z = (a + b + c) / 2;
	double zz = z * (z - a) * (z - b) * (z - c);
	return sqrt(zz);
}

double D(double x, double y, double xx, double yy){
	double k = pow(xx - x, 2) + pow(yy - y, 2);
	return sqrt(k);
}

int main(){
	double gnx, gny, x[2] = {}, y[2] = {}, ans = 0;
	char knm;
	cin >> gnx >> knm >> gny;
	x[0] = gnx;
	y[0] = gny;
	while (cin >> x[1] >> knm >> y[1]){
		double a, b, c;
		a = D(gnx, gny, x[0], y[0]);
		b = D(gnx, gny, x[1], y[1]);
		c = D(x[0], y[0], x[1], y[1]);
		double an = S(a, b, c);
		ans += an;
		x[0] = x[1];
		y[0] = y[1];
	}
	cout << ans << endl;
	return 0;
}