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 <stdio.h>
#include <math.h>

double Dis(double x1, double y1, double x2, double y2);

int main(void){
	double xs, ys;
	double x, y;
	double xb, yb;
	double dis1 = -1;
	double dis2 = -1;
	double dis3 = -1;
	double ans = 0;

	scanf("%lf,%lf", &xs, &ys);
	int i = 0;
	while(scanf("%lf,%lf", &x, &y) != EOF){
		if(i == 0){
			dis1 = Dis(x, y, xs, ys);
			xb = x;
			yb = y;
			i++;
			continue;
		}
		dis2 = Dis(x, y, xs, ys);
		dis3 = Dis(x, y, xb, yb);
		double z = (dis1 + dis2 + dis3) / 2.0;
		double s = sqrt(z*(z-dis1)*(z-dis2)*(z-dis3));
		ans += s;
		dis1 = dis2;
		xb = x;
		yb = y;
	}

	printf("%.7f\n", ans);

	return 0;
}

double Dis(double x1, double y1, double x2, double y2){
	return sqrt((y2-y1)*(y2-y1) + (x2-x1)*(x2-x1));
}