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;

int main(){
	double x[20], y[20], a, b, c, s = 0.0, z;
	int i;
	for (i = 0; i < 20; i++){
		if (scanf("%lf,%lf", &x[i], &y[i]) == EOF) break;
	}
	for (int j = 1; j < i - 1; j++){
		a = sqrt((x[j] - x[0]) * (x[j] - x[0]) + (y[j] - y[0]) * (y[j] - y[0]));
		b = sqrt((x[j + 1] - x[0]) * (x[j + 1] - x[0]) + (y[j + 1] - y[0]) * (y[j + 1] - y[0]));
		c = sqrt((x[j + 1] - x[j]) * (x[j + 1] - x[j]) + (y[j + 1] - y[j]) * (y[j + 1] - y[j]));
		z = (a + b + c) / 2.0;
		s += sqrt(z * (z - a) * (z - b) * (z - c));
	}
	printf("%.5f\n",s);
	return 0;
}