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<stdio.h>
#include<string.h>
#include<math.h>

int main(){
	double tyo[20][2],a,b,c,z,s;
	int n,i,j;
	
	s=0;
	n=0;
	while(~scanf("%lf,%lf",&tyo[n][0],&tyo[n][1])){
		++n;
	}
	
	for(i=1;i<n-1;i++){
		a=sqrt(pow(tyo[0][0]-tyo[i][0],2)+pow(tyo[0][1]-tyo[i][1],2));
		b=sqrt(pow(tyo[0][0]-tyo[i+1][0],2)+pow(tyo[0][1]-tyo[i+1][1],2));
		c=sqrt(pow(tyo[i+1][0]-tyo[i][0],2)+pow(tyo[i+1][1]-tyo[i][1],2));
		z=(a+b+c)/2;
		
		s+=sqrt(z*(z-a)*(z-b)*(z-c));
	}
	
	printf("%lf\n",s);
}