#include <iostream>
#include <stdio.h>
#include <iomanip>
using namespace std;

int main() {
	
	int n=0;
	double x[20],y[20],s=0;
	
	
	while(scanf("%lf,%lf",&x[n],&y[n])+1)
		++n;
	
	for(int i=0;i<n;++i){
		s += x[i]*y[(i+1)%n] - y[i]*x[(i+1)%n];
	}
	s/=2;
	
	cout<<setprecision(20)<<(s>0?s:-s)<<endl;
	return 0;
}
### Prompt

Please formulate a Cpp solution to 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 <iostream>
#include <stdio.h>
#include <iomanip>
using namespace std;

int main() {
	
	int n=0;
	double x[20],y[20],s=0;
	
	
	while(scanf("%lf,%lf",&x[n],&y[n])+1)
		++n;
	
	for(int i=0;i<n;++i){
		s += x[i]*y[(i+1)%n] - y[i]*x[(i+1)%n];
	}
	s/=2;
	
	cout<<setprecision(20)<<(s>0?s:-s)<<endl;
	return 0;
}
```