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 <cmath>
#include <cstdio>
using namespace std;

int main() {
	double x[3] = { .0 }, y[3] = { .0 }, sum = .0, z, a, b ,c;
	char t;

	cin >> x[0] >> t >> y[0] >> x[1] >> t >> y[1];
	while (cin >> x[2]) {
		cin >> t >> y[2];
		a = hypot(x[1] - x[0], y[1] - y[0]);
		b = hypot(x[2] - x[1], y[2] - y[1]);
		c = hypot(x[0] - x[2], y[0] - y[2]);
		z = (a + b + c) / 2;
		sum += sqrt(z * (z - a) * (z - b) * (z - c));
		x[1] = x[2], y[1] = y[2];
	}
	printf("%.6lf\n", sum);
	return 0;
}