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;
#define rep2(x,from,to) for(int x = (from); x < (to); ++(x))
#define rep(x,to) rep2(x,0,to)
int main() {
	double x[20], y[20];
	double a, b;
	int c = 0;
	char ch;
	while(cin >> a >> ch >> b) {
		x[c] = a, y[c] = b;
		c++;
	}
	double ret = 0;
	rep2(i,1,c-1) {
		double d = sqrt(pow(x[i]-x[0],2.0) + pow(y[i]-y[0],2.0));
		double e = sqrt(pow(x[i+1]-x[0],2.0) + pow(y[i+1]-y[0],2.0));
		double f = sqrt(pow(x[i]-x[i+1],2.0) + pow(y[i]-y[i+1],2.0));
		double z = (d+e+f)/2;
		ret += sqrt(z*(z-d)*(z-e)*(z-f));
	}
	printf("%.6lf\n", ret);
	return 0;
}