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<cmath>
using namespace std;
int main(){
  double x[3],y[3],s=0,z,a[3];
  char cc;
  cin>>x[0]>>cc>>y[0]>>x[1]>>cc>>y[1];
  for(int i=1;cin>>x[i%2+1]>>cc>>y[i%2+1];i++){
    z=0;
    for(int i=0;i<3;i++)a[i]= sqrt((x[i%3]-x[(i+1)%3])*(x[i%3]-x[(i+1)%3])+(y[i%3]-y[(i+1)%3])*(y[i%3]-y[(i+1)%3])),z+=a[i];
    z/=2;s += sqrt(z*(z-a[0])*(z-a[1])*(z-a[2]));
  }
  printf("%.7f\n",s);
}