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 <string>
#include <math.h>
#include <iomanip>
using namespace std;

int main()
{
	double x[21], y[21], a, b, c, z, s;
	char ch;
	int cnt = 1;
	s = 0;
	while (cin>>x[cnt]>>ch>>y[cnt])
	{
		cnt++;
	}

	for (int i = 1; i < cnt-1; i++)
	{
		a = sqrt((x[i] - x[1])*(x[i] - x[1]) + (y[i] - y[1])*(y[i] - y[1]));
		b = sqrt((x[i+1] - x[i])*(x[i+1] - x[i]) + (y[i+1] - y[i])*(y[i+1] - y[i]));
		c = sqrt((x[i+1] - x[1])*(x[i+1] - x[1]) + (y[i+1] - y[1])*(y[i+1] - y[1]));
		z = (a + b + c) / 2;
		s += sqrt(z*(z - a)*(z - b)*(z - c));
	}

	cout << fixed << setprecision(6) << s << endl;

	return 0;
}