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<cmath>
using namespace std;

int main()
{
	double x[3], y[3];
	double a, b, c, z, S;
	int i, j;

	cout<<setprecision(6);
	cout<<setiosflags(ios::fixed);
	S = 0;
	scanf("%lf,%lf", &x[0], &y[0]);
	scanf("%lf,%lf", &x[1], &y[1]);
	while (scanf("%lf,%lf", &x[2], &y[2]) != EOF) {
		a = sqrt( (x[1]-x[0])*(x[1]-x[0]) + (y[1]-y[0])*(y[1]-y[0]) );
		b = sqrt( (x[2]-x[1])*(x[2]-x[1]) + (y[2]-y[1])*(y[2]-y[1]) );
		c = sqrt( (x[0]-x[2])*(x[0]-x[2]) + (y[0]-y[2])*(y[0]-y[2]) );
		z = (a+b+c)/2.0;
		S += sqrt( z*(z-a)*(z-b)*(z-c) );
		x[1] = x[2];
		y[1] = y[2];
	}
	cout<<S<<endl;

	return 0;
}