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:
//32
#include<cstdio>
#include<cmath>
#include<complex>

using namespace std;

int main(){
  double x,y,px,py;
  scanf("%lf,%lf%lf,%lf",&x,&y,&px,&py);
  double s=0;
  complex<double> p(x,y),pp(px,py);
  for(double cx,cy;scanf("%lf,%lf",&cx,&cy)!=EOF;){
    complex<double> cp(cx,cy);
    double a=abs(pp-p),b=abs(cp-p),c=abs(cp-pp);
    double z=(a+b+c)/2;
    s+=sqrt(z*(z-a)*(z-b)*(z-c));
    pp=cp;
  }
  printf("%.6f\n",s);
  return 0;
}