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>
using namespace std;

typedef struct{
	double x, y;
}point;

double dist(point a, point b){
	return sqrt(pow(a.x-b.x, 2) + pow(a.y-b.y, 2));
}

int main(){
	point p[20];
	int n=0;
	double s;

	while( scanf(" %lf,%lf", &p[n].x, &p[n].y) != EOF) ++n;

	for(int i=1; i<=n-2; ++i){
		double a=dist(p[0], p[i]), b=dist(p[0], p[i+1]), c=dist(p[i], p[i+1]); 
		double z=(a+b+c)/2.0;
		s+=sqrt(z*(z-a)*(z-b)*(z-c));
	}

	printf("%lf\n", s);

	return 0;
}