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>

int n;
double x[21],y[21];

double fabs(double x){
	if(x<0)return -x;
	return x;
}

int main(void){
	while(~scanf("%lf,%lf",&x[n],&y[n]))n++;
	double sum=0.0;
	for(int i=0;i<n;i++)sum+=0.5*(x[i]-x[(i+1)%n])*(y[i]+y[(i+1)%n]);
	printf("%0.7f\n",fabs(sum));
	return 0;
}