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 <cstdio>
#include <complex>
#include <cmath>
using namespace std;
 
int main(int argc, char** argv) {
    double x, y;
    char c;
    cin >> x >> c >> y;
    complex<double> o(x, y);
    cin >> x >> c >> y;
    complex<double> a(x, y);
    a -= o;
    double s = 0.0;
    while(cin >> x >> c >> y) {
        complex<double> b(x, y);
        b -= o;
        s += 0.5*abs(a)*abs(b)*sin(abs(arg(a)-arg(b)));
        a = b;
    }
    printf("%.6f\n", s);
    return 0;
}