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

double area(pair<double,double> a, pair<double,double> b, pair<double,double> c){
	double d1 = sqrt( pow(a.first-b.first,2) + pow(a.second-b.second,2) );
	double d2 = sqrt( pow(c.first-b.first,2) + pow(c.second-b.second,2) );
	double d3 = sqrt( pow(a.first-c.first,2) + pow(a.second-c.second,2) );
	double s = (d1+d2+d3)/2.0;
	return sqrt( s*(s-d1)*(s-d2)*(s-d3) );
}

int main(){
	double x,y;
	vector<pair<double,double> > vec;
	while(scanf("%lf,%lf",&x,&y) != EOF){
		vec.push_back(make_pair(x,y));
	}
	double rta = 0;
	for(int x=1;x<vec.size()-1;++x){
		rta += area(vec[0],vec[x],vec[x+1]);
	}
	
	printf("%.8lf\n",rta);
}