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 <cmath>
#include <cstdio>

using namespace std;

int main() {

	int n=0;
	double S=0, x[20], y[20];

	while(scanf("%lf, %lf", &x[n], &y[n])!=EOF) {
		n++;
	}
	for(int i=1; i<n-1; i++) {
		double a=sqrt(pow(x[0]-x[i], 2)+pow(y[0]-y[i], 2));
		double b=sqrt(pow(x[i]-x[i+1], 2)+pow(y[i]-y[i+1], 2));
		double c=sqrt(pow(x[i+1]-x[0], 2)+pow(y[i+1]-y[0], 2));
		double z=(a+b+c)/2;
		S+=sqrt(z*(z-a)*(z-b)*(z-c));
	}

	printf("%.6f\n", S);

	return 0;

}