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 <vector>
#include <math.h>
#include <iomanip>
using namespace std;

int main() {

  vector< double > x, y;
  double in_x, in_y;
  char in_c;

  while( cin >> in_x >> in_c >> in_y ) {

    x.push_back( in_x );
    y.push_back( in_y );

  }

  double ans = 0.00;

  for( long long int i = 0; i < x.size() - 2; i++ ) {

    double mx = x[0] - x[i+1];
    double my = y[0] - y[i+1];
    double a = sqrt( mx*mx + my*my );
    mx = x[0] - x[i+2];
    my = y[0] - y[i+2];
    double b = sqrt( mx*mx + my*my );
    mx = x[i+1] - x[i+2];
    my = y[i+1] - y[i+2];
    double c = sqrt( mx*mx + my*my );
    double z = ( a + b + c ) / 2;

    ans += sqrt(z*(z-a)*(z-b)*(z-c));

  }

  cout << fixed << setprecision(8) << ans << endl;
  return 0;

}