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>
using namespace std;

#define rep(i,n) for(int i=0;i<n;i++)
#define ll long long

int main()
{
    double x1,x2,x3,y1,y2,y3,r=0,a,b,c;
    scanf("%lf,%lf",&x1,&y1);
    scanf("%lf,%lf",&x2,&y2);
    while(scanf("%lf,%lf",&x3,&y3) != EOF)
    {
	a=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
	b=sqrt((x3-x2)*(x3-x2)+(y3-y2)*(y3-y2));
	c=sqrt((x1-x3)*(x1-x3)+(y1-y3)*(y1-y3));
	r+=sqrt((a+b+c)/2*(b+c-a)/2*(a-b+c)/2*(a+b-c)/2);
	x2=x3;
	y2=y3;
    }
    printf("%.6f\n",r);
    return 0;
}