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(){
	int cnt = 0;
	double x1, x2, x3, y1, y2, y3, s = 0.0;
	char c;

	while ( cin >> x3 >> c >> y3 ){
		++cnt;
		if ( cnt == 1 ){
			x1 = x3;
			y1 = y3;
		}
		if ( cnt >= 3 ){
			double a = sqrt( pow( x2 - x1, 2.0 ) + pow( y2 - y1, 2.0 ) );
			double b = sqrt( pow( x3 - x2, 2.0 ) + pow( y3 - y2, 2.0 ) );
			double c = sqrt( pow( x1 - x3, 2.0 ) + pow( y1 - y3, 2.0 ) );
			double z = ( a + b + c ) / 2;
			s += sqrt( z * ( z - a ) * ( z - b ) * ( z - c ) );
		}

		x2 = x3;
		y2 = y3;
	}

	cout << setprecision( 6 ) << setiosflags( ios::fixed );
	cout << s << endl;

	return 0;
}