#include <complex>
#include <cmath>
#include <stdio.h>
using namespace std;
typedef complex<double> xy_t;

xy_t P[110];

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

int main(){
	int N = 0;
	double x, y;
	while (~scanf("%lf,%lf", &x, &y)) {
		P[N++] = xy_t(x,y);
	}
	double sum = 0.0;
	for (int i = 0; i+2 < N; i++) {
		xy_t a = P[0], b = P[i+1], c = P[i+2];
		sum += (cross_product(a-b,c-b))/2;
	}
	printf("%.6f\n",abs(sum));
}
 
### Prompt

Develop a solution in cpp to the problem described below:

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 <complex>
#include <cmath>
#include <stdio.h>
using namespace std;
typedef complex<double> xy_t;

xy_t P[110];

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

int main(){
	int N = 0;
	double x, y;
	while (~scanf("%lf,%lf", &x, &y)) {
		P[N++] = xy_t(x,y);
	}
	double sum = 0.0;
	for (int i = 0; i+2 < N; i++) {
		xy_t a = P[0], b = P[i+1], c = P[i+2];
		sum += (cross_product(a-b,c-b))/2;
	}
	printf("%.6f\n",abs(sum));
}
 
```