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<iostream>
#include<cmath>
#include<stdio.h>
using namespace std;

double ans=0.0,x[1000],y[1000];
int id;
char ch;

double S3(double ,double,double,double,double,double);
double f(double,double,double,double);
int main(){
  id=0;
  while(cin>>x[id]>>ch>>y[id]){
    if(id>=2){
      ans+=S3(x[0],y[0],x[id-1],y[id-1],x[id],y[id]);
    }
    id++;   
  }
  //  cout<<ans<<endl;
  printf("%.6f\n",ans);
  return 0;
  
}


double S3(double x1,double y1,double x2,double y2,double x3,double y3){
  double a=f(x1,y1,x2,y2),b=f(x2,y2,x3,y3),c=f(x3,y3,x1,y1);
  double z=(a+b+c)/2.0;
  return sqrt(z*(z-a)*(z-b)*(z-c));
}


double f(double x1,double y1,double x2,double y2){
  return sqrt(pow(x1-x2,2.0)+pow(y1-y2,2.0));

}