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

Solution (in CPP):

Solution:
#include <iostream>
#include <vector>
#include <complex>
#include <iomanip>

using namespace std;

typedef complex<double> point;

double cross(point a,point b){
    return imag(conj(a)*b);
}

double triangle_area(point a,point b,point c){
    return cross(b-a,c-a)/2;
}

double vertex_area(vector<point> v){
    double ret = 0;
    for(int i=1;i<v.size()-1;i++){
        ret += triangle_area(v[0],v[i],v[i+1]);
    }
    return ret;
}

int main(){
    cout << fixed << setprecision(10);
    vector<point> v;
    double x,y;
    char c;
    while(cin >> x >> c >> y){
        v.push_back(point(x,y));
    }
    cout << abs(vertex_area(v)) << endl;
    return 0;
}