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 <complex>
#include <cmath>
using namespace std;
typedef complex<double> xy_t;
double cross_product(xy_t a, xy_t b) {
    return(conj(a)*b).imag(); 
}

int main() {
    xy_t p[30];
    double x, y;
    char c;
    int idx = 0;
    while (cin >> x >> c >> y) {
        p[idx] = xy_t(x, y);
        idx++;
    }

    double sm = 0.0;
    for (int i = 0; i < idx - 2; i++) {
        xy_t a = p[0], b = p[i + 1], c = p[i + 2];
        sm += cross_product(b - a, c - a) / 2.0;
    }

    cout << sm << endl;
}

/*
g++ -std=c++14 pr_prog/_main.cpp
 */