#include<complex>
#include<cmath>
#include<iostream>
#include<cstdio>
using namespace std;
typedef complex<double> xy_t;
xy_t P[110];
double z;
int n=0;
double x,y;
double sum=0.0;
double menseki(xy_t a,xy_t b, xy_t c){
    return a.real()*(b.imag()-c.imag())+b.real()*(c.imag()-a.imag())+c.real()*(a.imag()-b.imag());
}
int main(){
    while (scanf("%lf,%lf", &x, &y) != EOF) {
        P[n++]=xy_t(x,y);
    }
    for(int i=0;i+2<n;i++){
        xy_t a=P[0],b=P[i+1],c=P[i+2];
        sum+=menseki(a,b,c)/2;
    }
    printf("%.6f\n",abs(sum));
    return 0;
}



### 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<iostream>
#include<cstdio>
using namespace std;
typedef complex<double> xy_t;
xy_t P[110];
double z;
int n=0;
double x,y;
double sum=0.0;
double menseki(xy_t a,xy_t b, xy_t c){
    return a.real()*(b.imag()-c.imag())+b.real()*(c.imag()-a.imag())+c.real()*(a.imag()-b.imag());
}
int main(){
    while (scanf("%lf,%lf", &x, &y) != EOF) {
        P[n++]=xy_t(x,y);
    }
    for(int i=0;i+2<n;i++){
        xy_t a=P[0],b=P[i+1],c=P[i+2];
        sum+=menseki(a,b,c)/2;
    }
    printf("%.6f\n",abs(sum));
    return 0;
}



```