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.

<image>



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<complex>
#include<vector>
using namespace std;
typedef complex<double> P;

double length(P a,P b){
    double t=2;
    return sqrt(pow(a.real()-b.real(),t)+pow(a.imag()-b.imag(),t));
}

double heron(double a, double b, double c){
    double z = (a+b+c)/2;
    return sqrt(z*(z-a)*(z-b)*(z-c));
}

int main(){
    vector<P> p(20);
    double x, y;
    int i=0;
    while(scanf("%lf,%lf", &x, &y) != EOF){
        p[i] = P(x,y);
        i++;
    }
    double sum = 0;
    for(int j = 1; j < i-1; j++){
        sum += heron(length(p[0], p[j]), length(p[j], p[j+1]), length(p[j+1], p[0]));
    }
    printf("%.6lf\n", abs(sum));
}