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<cstdio>
typedef struct{
  double x,y;
}space;
using namespace std;
#define loop(i,a,b) for(int i=a;i<b;i++)
#define rep(i,a) loop(i,0,a)
int main(){
  space in[21];
  char m;
  rep(i,2)cin>>in[i].x>>m>>in[i].y;
  double d,e;
  int i=1;
  double sum=0;
  while(cin>>d>>m>>e){
    double a=hypot(in[0].x-in[i].x,in[i].y-in[0].y);
    double b=hypot(d-in[i].x,in[i].y-e);
    double c=hypot(in[0].x-d,e-in[0].y);
    double z=(a+b+c)/2;
    sum+=sqrt(z*(z-a)*(z-b)*(z-c));
    in[i+1].x=d;
    in[i+1].y=e;
    i++;
    //cout<<sum<<endl;
  }
  printf("%.10f\n",sum);
}