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 <stdio.h>
#include <math.h>
using namespace std;

#define rep(x,to) for(int i=x;i<to;i++)

double lengths(double x1,double x2,double y1,double y2){
	return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
}

int main() {
	int n=1,i=0;
	double x[25]={},y[25]={},lengthA[25],lengthB[25],lengthC,S=0,z;
	while(1){
		if(scanf("%lf,%lf\n",&x[i],&y[i])==EOF){
			n--;
			break;
		} 
		i++;
		n++;
	}
	rep(0,n-1){
		lengthA[i] = lengths(x[0],x[i+1],y[0],y[i+1]);
//		printf("%.6f\n",lengthA[i]);
	}
	rep(0,n-2)	lengthB[i] = lengths(x[i+1],x[i+2],y[i+1],y[i+2]);
		
	rep(0,n-2){ //３辺を用いた面積計算
		lengthC = lengthA[i+1];
		z = (lengthA[i]+lengthB[i]+lengthC)/2.0;
		S += sqrt(z*(z-lengthA[i])*(z-lengthB[i])*(z-lengthC));
	}
	printf("%.7f\n",S);
	return 0;
}