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 <sstream>
#include <string>
#include <algorithm>
#include <vector>
#include <iomanip>
#include <queue>
#include <set>
#include <map>
#include <cstdlib>
#include <cstdio>
#include <cmath>
#include <bitset>
#include <complex>
using namespace std;

const double EPS = 1e-9;
const double PI = 3.14159265359;

typedef complex<double> p;

double GetArea(p a, p b, p c){
	double la, lb, lc, lz;
	la = abs(b-a);
	lb = abs(c-b);
	lc = abs(a-c);
	lz = (la+lb+lc)/2;

	return sqrt(lz*(lz-la)*(lz-lb)*(lz-lc));
}

int main(){
	double x, y;
	vector<p> pv;

	while(~scanf("%lf,%lf", &x, &y)){
		pv.push_back(p(x, y));
	}

	double s = 0.0;
	for(int i = 0; i+1 < pv.size(); i++){
		s += GetArea(pv[0], pv[i], pv[i+1]);
	}

	printf("%lf", s);

	return 0;
}