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 <cstdio>
#include <complex>
#include <cmath>
#include <vector>
using namespace std;

typedef complex<double> P;

double cross(P a, P b){
	return real(a) * imag(b) - imag(a) * real(b);
}

int main(){
	double x, y;
	vector<P> v;
	while(scanf("%lf,%lf", &x, &y) != EOF){
		v.push_back(P(x, y));
	}
	double s = 0.0;
	for(int i = 0; i < v.size(); ++i){
		s += cross(v[i], v[(i + 1) % v.size()]);
	}
	printf("%.10f\n", 0.5 * abs(s));
}