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<cstdio>
#include<algorithm>
#include<cmath>
using namespace std;
int main()
{
	double xs[20],ys[20];
	int cnt=0;
	while(scanf("%lf,%lf",&xs[cnt],&ys[cnt])!=EOF) 
	{
		++cnt;
	}

	int mid=1;
	double ans=0;
	while(mid+1<cnt) 
	{
		double a=sqrt( (xs[mid]-xs[0])*(xs[mid]-xs[0])+(ys[mid]-ys[0])*(ys[mid]-ys[0]) );
		double b=sqrt( (xs[mid]-xs[mid+1])*(xs[mid]-xs[mid+1])+(ys[mid]-ys[mid+1])*(ys[mid]-ys[mid+1]) );
		double c=sqrt( (xs[mid+1]-xs[0])*(xs[mid+1]-xs[0])+(ys[mid+1]-ys[0])*(ys[mid+1]-ys[0]) );
		double z=(a+b+c)/2;
		ans+=sqrt(z*(z-a)*(z-b)*(z-c));
		mid++;
	}
	printf("%.9lf\n",ans);
  return 0;
}