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 <bits/stdc++.h>
#define range(i,a,b) for(int (i)=(a);(i)<(b);(i)++)
#define rep(i,n) range(i,0,n)
using namespace std;

double x[25],y[25];

inline double dist(int i,int j){
	double xx=x[j]-x[i];
	double yy=y[j]-y[i];
	return sqrt(xx*xx+yy*yy);
}

double area(double a,double b,double c){
	double s=(a+b+c)/2.0;
	return sqrt(s*(s-a)*(s-b)*(s-c));
}

int main(void){
	double s=0.0;
	int n=0;
	char tmp;
	while(cin >> x[n] >> tmp >> y[n]){
		if(cin.eof()) break;
		n++;
	}
	range(i,2,n){
		double a=dist(0,i-1);
		double b=dist(0,i);
		double c=dist(i-1,i);
		s+=area(a,b,c);
	}
	cout.precision(10);
	cout << fixed << s << endl;
	return 0;
}