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 <complex>
#include <cmath>
using namespace std;
typedef complex<double> xy_t;
xy_t P[21];
double area(xy_t A, xy_t B,xy_t C)
{
  double a=abs(B-C);
  double b=abs(A-C);
  double c=abs(A-B);
  double z=(a+b+c)/2.0;
  return sqrt(z*(z-a)*(z-b)*(z-c));
}
int main()
{
  int N=0;
  double x,y;
  while(scanf("%lf,%lf",&x,&y)!=EOF)
  {
    P[N++]=xy_t(x,y);
  }
  double sum=0.0;
  for(int i=1;i<N-1;i++)
  {
    sum+=area(P[0],P[i],P[i+1]);
  }
  printf("%6lf\n",sum);
  return 0;
}