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 <iomanip>
using namespace std;

struct point{double px; double py;};

double x, y, s;
int i,j;

int main(){
	point p[21];	
	char k;

	while(cin>>x>>k>>y){
		if(cin.eof())break;
		p[i].px = x;
		p[i].py = y;
		i++;
	}
	p[i].px = p[0].px;
	p[i].py = p[0].py;

	for(; j<i; j++)	s += (p[j].px-p[j+1].px)*(p[j].py+p[j+1].py);

	cout<<setiosflags(ios::fixed)<<setprecision(6)<<s/2<<"\n";
	return 0;
}