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 <cmath>
using namespace std;

inline double alength(double x1,double y1,double x2,double y2){
  return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
}

int main(void){
  double x[20],y[20];
  int i=0;
  double S=0.0;
  while(scanf("%lf,%lf",&x[i],&y[i])!=EOF)++i;
  for(int p=1;p<i-1;++p){
      double a=alength(x[0],y[0],x[p],y[p]);
      double b=alength(x[p],y[p],x[p+1],y[p+1]);
      double c=alength(x[p+1],y[p+1],x[0],y[0]);
      double s=(a+b+c)/2.0;
      double dS=sqrt(s*(s-a)*(s-b)*(s-c));
      S+=dS;
    }
  printf("%.6f\n",S);
  return 0;
}