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 JAVA):

Solution:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;

class Main {

	/*
	 * https://onlinejudge.u-aizu.ac.jp/problems/0079
	 */

	public static void main(String[] args) throws IOException {
		//入力
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		ArrayList<double[]> points = new ArrayList<>();
		String str = br.readLine();
		for(; str!=null; str=br.readLine()) {
			String s[] = str.trim().split(",");
			double p[] = {Double.parseDouble(s[0]), Double.parseDouble(s[1])};
			points.add(p);
		}

		//0番目の点が原点になるように平行移動
		double originX = points.get(0)[0],
		       originY = points.get(0)[1];
		for(int i=0; i<points.size(); i++) {
			double p1[] = points.get(i);
			p1[0] -= originX;
			p1[1] -= originY;
		}
		//外積の半分を計算して足す
		double area = 0;
		for(int i=1; i+1<points.size(); i++) {
			area += crossProduct(points.get(i), points.get(i+1))/2;
			//System.out.println(area);
		}
		//area += crossProduct(points.get(points.size()-1), points.get(1)); <- これは要らない

		//出力
		System.out.println(Math.abs(area));
	}

	//外積を計算
	private static double crossProduct(double[] v1, double[] v2) {
		return v1[0]*v2[1]-v1[1]*v2[0];
	}

}