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:
/*
	0079:Area of Polygon
*/
#include	<iostream>
#include	<vector>
#include	<utility>
#include	<cstdio>

using namespace std;

typedef pair<double, double> P_DD;

int main(void) {
	double x, y, sx, sy, sum = 0.0;
	vector<P_DD> data;
	bool fir = true;
	
	while( scanf("%lf,%lf", &x, &y) != EOF) {
		if(fir) {
			sx = x;	sy = y;
			fir = false;
		}
		data.push_back( P_DD(x, y) );
	}
	data.push_back( P_DD(sx, sy) );
	
	vector<P_DD>::iterator it = data.begin();
	
	while( it+1 != data.end() ) {
		double b1x = (*it).first, b1y = (*it).second, b2x = (*(it+1)).first, b2y = (*(it+1)).second;
		
		sum += (b1x - b2x) * (b1y + b2y);
		it++;
	}
	sum /= 2;
	if(sum < 0) { sum *= -1.0; }
	printf("%f\n", sum);
	
	return 0;
}