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<cmath>

struct Point{ double x, y;};

double getDistance(Point p1, Point p2){
    return sqrt( (p1.x-p2.x)*(p1.x-p2.x) + (p1.y-p2.y)*(p1.y-p2.y));
}
int main(){
    Point P[20];
    int n = 0;
    double z, S = 0;
    while( scanf("%lf,%lf", &P[n].x, &P[n].y) != EOF ){
	n++;
    }
    for ( int i = 1; i < n-1; i++ ){
	double a = getDistance(P[0], P[i]);
	double b = getDistance(P[i], P[i+1]);
	double c = getDistance(P[0], P[i+1]);
	z = (a + b + c )/2.0;
	S += sqrt(z*(z-a)*(z-b)*(z-c));
    }
    printf("%.8lf\n", S);
}