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


double dot_product(xy_t a, xy_t b){
        return (conj(a)*b).real();
}

double cross_product(xy_t a, xy_t b){
        return (conj(a)*b).imag();
}
int main(){
        xy_t o,a,b;
        double sum = 0,x,y;
        scanf("%lf,%lf", &x, &y);
        o = xy_t (x, y);
        scanf("%lf,%lf", &x, &y);
        a = xy_t (x, y) - o;
        b = a;
        while(~scanf("%lf,%lf", &x, &y)){
                a = xy_t (x, y) - o;
                sum += cross_product(a,b) / 2.0;
                b = a;
        }
        printf("%.6f\n", abs(sum));
return 0;
}
### Prompt

Please create a solution in CPP 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 <complex>
#include <cmath>
using namespace std;
typedef complex<double> xy_t;


double dot_product(xy_t a, xy_t b){
        return (conj(a)*b).real();
}

double cross_product(xy_t a, xy_t b){
        return (conj(a)*b).imag();
}
int main(){
        xy_t o,a,b;
        double sum = 0,x,y;
        scanf("%lf,%lf", &x, &y);
        o = xy_t (x, y);
        scanf("%lf,%lf", &x, &y);
        a = xy_t (x, y) - o;
        b = a;
        while(~scanf("%lf,%lf", &x, &y)){
                a = xy_t (x, y) - o;
                sum += cross_product(a,b) / 2.0;
                b = a;
        }
        printf("%.6f\n", abs(sum));
return 0;
}
```