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 <iomanip>
#include <cmath>

using namespace std;

int main()
{
    double area = 0.0;
    double x[20], y[20];
    int n = 0;
    char ch;

    while (cin >> x[n] >> ch >> y[n])
        n++;
    x[n] = x[0];
    y[n] = y[0];
    n++;

    for (int i = 0; i < n; i++)
        area += x[i] * y[i + 1] - x[i + 1] * y[i];

    cout << setiosflags(ios::fixed) << setprecision(6);
    cout << abs(area  / 2.0) << endl;
}