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.

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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<cstdio>
#include<vector>
#include<cmath>
using namespace std;
typedef pair<double,double> P;
double po(double d){return d*d;}
int main(){
    vector<P> ps;
    double x,y;
    while(scanf("%lf,%lf\n",&x,&y)!=-1){
        ps.push_back(make_pair(x,y));
    }
    double s=0;
    for(int i=1;i+1<ps.size();i++){
        double x[3],y[3];
        x[0]=ps[0].first;
        x[1]=ps[i].first;
        x[2]=ps[i+1].first;
        y[0]=ps[0].second;
        y[1]=ps[i].second;
        y[2]=ps[i+1].second;
        double a=sqrt(po(x[0]-x[1])+po(y[0]-y[1])),b=sqrt(po(x[1]-x[2])+po(y[1]-y[2])),c=sqrt(po(x[2]-x[0])+po(y[2]-y[0])),z=(a+b+c)/2;
        s+=sqrt(z*(z-a)*(z-b)*(z-c));
    }
    printf("%lf\n",s);
}