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>
using namespace std;

int main(){
    double x[20], y[20], area = 0;
    int i = 0;
    while( scanf("%lf,%lf", &x[i], &y[i]) != EOF) i++;
    for(int j = 2; j < i; j++){
        double dx1 = x[j]-x[0], dy1 = y[j]-y[0];
        double dx2 = x[j-1]-x[0], dy2 = y[j-1]-y[0];
        double dx3 = x[j]-x[j-1], dy3 = y[j]-y[j-1];
        double a = sqrt(dx1*dx1+dy1*dy1);
        double b = sqrt(dx2*dx2+dy2*dy2);
        double c = sqrt(dx3*dx3+dy3*dy3);
        double z = (a+b+c)/2;
        area += sqrt(z*(z-a)*(z-b)*(z-c));
    }
    printf("%.6lf\n", abs(area));
    return 0;
}