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

double triangle(double p1x,double p1y,double p2x,double p2y, double p3x, double p3y);

struct Point{
  double x;
  double y;
}typedef point;

int main(void){
  double x,y;
  vector<point> v;
  while(scanf("%lf,%lf",&x,&y)!=EOF){
    point p;
    p.x=x;
    p.y=y;
    v.push_back(p);
  }
  int n=v.size();
  double area=0;
  for(int i=1;i<n-1;i++){
    area+=triangle(v[0].x,v[0].y,v[i].x,v[i].y,v[i+1].x,v[i+1].y);
  }
  cout<<abs(area)<<endl;
  return 0;
}


double triangle(double p1x,double p1y,double p2x,double p2y, double p3x, double p3y){
  p2x-=p1x;
  p3x-=p1x;
  p2y-=p1y;
  p3y-=p1y;
  return -1*((double)(p2x*p3y-p3x*p2y))/2;
}