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>
#include <cstdio>

using namespace std;

double r(double x1[2], double x2[2]){
        return pow(pow(x1[0]-x2[0],2)+pow(x1[1]-x2[1],2),0.5);
}
int main(){
        int n = 0;
        char c;
        double x[20][2];
        double s = 0;
        while(cin >> x[n][0] >> c >> x[n][1]) ++n;
        for(int i = 1; i < n-1; i++){
                double d[3] = {0};
                d[0] = r(x[0],x[i]);
                d[1] = r(x[0],x[i+1]);
                d[2] = r(x[i],x[i+1]);
                double z = (d[0]+d[1]+d[2])/2;
                s += pow(z*(z-d[0])*(z-d[1])*(z-d[2]),0.5);
        }   
        printf("%.6f\n",s);
}