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


int main(){
	char _;	
	int n=0;
	double x[21],y[21];
	while(cin>>x[n]>>_>>y[n])n++;
	x[n]=x[0];y[n]=y[0];
	double s=0;
	for(int i=0;i<n;i++){
		s += x[i]*y[i+1] - y[i]*x[i+1];
	}
	printf("%.6f\n",abs(s/2));
	return 0;
}
### Prompt

Create a solution in Cpp for 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<cstdio>
#include<cmath>
using namespace std;


int main(){
	char _;	
	int n=0;
	double x[21],y[21];
	while(cin>>x[n]>>_>>y[n])n++;
	x[n]=x[0];y[n]=y[0];
	double s=0;
	for(int i=0;i<n;i++){
		s += x[i]*y[i+1] - y[i]*x[i+1];
	}
	printf("%.6f\n",abs(s/2));
	return 0;
}
```