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<cmath>
#include<cstdio>
using namespace std;
int main(){
	double point[30][2],s = 0;
	int i;
	for(i=0;;i++){
		if(scanf("%lf,%lf",&point[i][0],&point[i][1]) == EOF){break;}
	}
	for(int j=1; j<i-1; j++){
		double z,a,b,c;
		a = sqrt((point[j][0]-point[0][0])*(point[j][0]-point[0][0])+(point[j][1]-point[0][1])*(point[j][1]-point[0][1]));
		b = sqrt((point[j+1][0]-point[0][0])*(point[j+1][0]-point[0][0])+(point[j+1][1]-point[0][1])*(point[j+1][1]-point[0][1]));
		c = sqrt((point[j+1][0]-point[j][0])*(point[j+1][0]-point[j][0])+(point[j+1][1]-point[j][1])*(point[j+1][1]-point[j][1]));
		z = (a+b+c)/2;
		s+=sqrt(z*(z-a)*(z-b)*(z-c));
	}
	printf("%.6lf\n",s);
	return 0;
}