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 <cstdio>
#include <cmath>
#define SQ(x) (x)*(x)

using namespace std;

double dis(double x1,double x2,double y1,double y2){
  return(sqrt(SQ(x2-x1)+SQ(y2-y1)));
}

int main(void){
  int n=0;
  double k[20][2],s=0;
  char c;
  while(cin>>k[n][0]>>c>>k[n][1])n++;
  for(int i=1;i<n-1;i++){
    double a=dis(k[0][0],k[i][0],k[0][1],k[i][1]);
    double b=dis(k[i][0],k[i+1][0],k[i][1],k[i+1][1]);
    double c=dis(k[0][0],k[i+1][0],k[0][1],k[i+1][1]);
    double z=(a+b+c)/2;
    s+=sqrt(z*(z-a)*(z-b)*(z-c));
  }
  printf("%.6lf\n",s);
  return 0;
}