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 <cmath>
#include <cstdio>
#include <vector>

using namespace std;

vector<pair<double,double> > v;

double s(double x1, double y1, double x2, double y2, double x3, double y3){
  double a,b,c,z;

  a = sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
  b = sqrt((x1-x3)*(x1-x3)+(y1-y3)*(y1-y3));
  c = sqrt((x2-x3)*(x2-x3)+(y2-y3)*(y2-y3));

  z = (a+b+c)/2;

  return sqrt(z*(z-a)*(z-b)*(z-c));
}

int main(void){
  int n=0;
  double x,y;
  double ret=0;

  while(cin >> x){
	cin.ignore();
	cin >> y;
	v.push_back(make_pair(x,y));
	n++;
  }
  
  for(int i=0;i<n-2;i++){
	ret += s(v[0].first, v[0].second, v[i+1].first,
			 v[i+1].second, v[i+2].first, v[i+2].second);
  }

  printf("%.7f\n", ret);
}