#include <cstdio>
#include <complex>
#include <cmath>
#include <vector>

using namespace std;

typedef complex<double> xy_t;

double cross_product(xy_t a, xy_t b) {
	return (conj(a) * b).imag();
}

int main() {
	double x, y;
	double s = 0;
	vector<xy_t> vertex;
	while (scanf("%lf,%lf", &x, &y) != EOF) {
		vertex.push_back(xy_t(x, y));
	}
	for (int i = 1; i < vertex.size() - 1; i++) {
		s += cross_product(vertex[i] - vertex[0], vertex[i + 1] - vertex[0]) / 2;
	}
	printf("%.6f", abs(s));
}
### Prompt

In Cpp, your task is to solve the following 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.

<image>



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

### Response

```cpp
#include <cstdio>
#include <complex>
#include <cmath>
#include <vector>

using namespace std;

typedef complex<double> xy_t;

double cross_product(xy_t a, xy_t b) {
	return (conj(a) * b).imag();
}

int main() {
	double x, y;
	double s = 0;
	vector<xy_t> vertex;
	while (scanf("%lf,%lf", &x, &y) != EOF) {
		vertex.push_back(xy_t(x, y));
	}
	for (int i = 1; i < vertex.size() - 1; i++) {
		s += cross_product(vertex[i] - vertex[0], vertex[i + 1] - vertex[0]) / 2;
	}
	printf("%.6f", abs(s));
}
```