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

struct rec{
	double x,y;
};

int main(){
	
	int n;
	struct rec dot[21]={0};
	double ans=0,a,b,c,z;
	
	for(int i=0;i<20;i++){
		if(scanf("%lf,%lf",&dot[i].x,&dot[i].y)==EOF){
			n=i;
			break;
		}
	}
	
	for(int i=0;i<n-2;i++){
		a=sqrt(pow(dot[0].x-dot[i+1].x,2)+pow(dot[0].y-dot[i+1].y,2));
		b=sqrt(pow(dot[i+1].x-dot[i+2].x,2)+pow(dot[i+1].y-dot[i+2].y,2));
		c=sqrt(pow(dot[i+2].x-dot[0].x,2)+pow(dot[i+2].y-dot[0].y,2));
		
		z=(a+b+c)/2;
		
		ans=ans+sqrt(z*(z-a)*(z-b)*(z-c));
	}
	
	printf("%.6lf\n",ans);
	
	return 0;
}