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<cstdio>
#include<cmath>

struct P{
	double x, y;
};

struct Triangle{
	P A, B, C;
};

double distance(P p1, P p2){
	double dx = p1.x - p2.x,
		dy = p1.y - p2.y;
	return sqrt(dx*dx+dy*dy);
}

double getArea(Triangle t){
	double a = distance(t.B, t.C),
		b = distance(t.A, t.C),
		c = distance(t.A, t.B),
		s = (a+b+c) / 2;
	return sqrt(s*(s-a)*(s-b)*(s-c));
}

int main(){
	P ps[21];
	int n = 0;
	for(;~scanf("%lf,%lf", &ps[n].x, &ps[n].y);n++){}
	double S = 0;
	for(int i=2;i<n;i++){
		Triangle t = {ps[0], ps[i-1], ps[i]};
		S += getArea(t);
	}
	printf("%.6f\n", S);
}