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 <iostream>
#include <cmath>
#include <cstdlib>
using namespace std;
struct P{
	double x,y;
};
P p[100];
double func(int i){
	double a = sqrt((p[0].x - p[i-1].x)*(p[0].x - p[i-1].x)+(p[0].y - p[i-1].y)*(p[0].y - p[i-1].y));
	double b = sqrt((p[0].x - p[i].x)*(p[0].x - p[i].x)+(p[0].y - p[i].y)*(p[0].y - p[i].y));
	double c = sqrt((p[i].x - p[i-1].x)*(p[i].x - p[i-1].x)+(p[i].y - p[i-1].y)*(p[i].y - p[i-1].y));
	double z = (a + b + c)/2;
	return sqrt(z*(z-a)*(z-b)*(z-c));
}
int main(){
	double x,y;
	int cnt = 0;
	while(~scanf("%lf,%lf",&p[cnt].x,&p[cnt].y)){
		cnt++;
	}
	double ans = 0;
	for(int i = 2; i < cnt; i++){
		ans += func(i);
	}
	printf("%.6lf\n",ans);
}