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<algorithm>
#include<string>
#include<stack>
#include<queue>
#include<complex>
#include<cmath>
using namespace std;
typedef complex<double> comp;

double crs_prod(comp a, comp b) { return (conj(a)*b).imag(); }

double c1, c2;
double area = 0;
comp z[20];
int n = 0;
int main(){
	while(~scanf("%lf,%lf", &c1, &c2)){
		z[n] = comp(c1, c2);
		n++;
	}
	for(int i=1; i<n-1; i++){
		area += crs_prod(z[i]-z[0], z[i+1]-z[0])/2;
	}
	printf("%f",area>0 ? area : -area);
	return 0;
}