#include<iostream>
#include<complex>
#include<cmath>
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,s=0.0;
    xy_t a,b,c;
    while(~scanf("%lf,%lf",&x,&y)){
        p[n]=xy_t(x,y);
        n++;
        //cout<<p[n]<<endl;
    }
    a=p[0];
    for(int i=0;i<n-2;i++){
        b=p[i+1],c=p[i+2];
        s+=cross_product(b-a,c-a)/2;
        //cout<<b<<c<<s<<endl;
    }
    cout<<abs(s)<<endl;
}

### Prompt

Construct a cpp code solution to the problem outlined:

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<complex>
#include<cmath>
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,s=0.0;
    xy_t a,b,c;
    while(~scanf("%lf,%lf",&x,&y)){
        p[n]=xy_t(x,y);
        n++;
        //cout<<p[n]<<endl;
    }
    a=p[0];
    for(int i=0;i<n-2;i++){
        b=p[i+1],c=p[i+2];
        s+=cross_product(b-a,c-a)/2;
        //cout<<b<<c<<s<<endl;
    }
    cout<<abs(s)<<endl;
}

```