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 <algorithm>
#include <cstdio>
#include <vector>
#include <complex>
using namespace std;

//---------------------------------------------------------------
using P = complex<double>;
double dot(const P& a, const P& b) { return real(conj(a) * b); }
double cross(const P& a, const P& b) { return imag(conj(a) * b); }
//---------------------------------------------------------------

int main() {
    vector<P> ps;
    double x, y;
    while (~scanf("%lf,%lf", &x, &y)) {
        ps.emplace_back(x, y);
    }
    double sum = 0;
    P a = ps[0];
    for (int i = 0; i < ps.size() - 2; i++) {
        P b = ps[i + 1], c = ps[i + 2];
        sum += cross(b - a, c - a) / 2;
    }
    printf("%.6f\n", abs(sum));
    return 0;
}