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 <complex>
#include <cmath>
#include <cstdio>
using namespace std;
typedef complex<double> xy_t;

double dot_product(xy_t a, xy_t b) { return (conj(a) * b).real(); }
double cross_product(xy_t a, xy_t b) { return (conj(a) * b).imag(); }
xy_t projection(xy_t p, xy_t b) { return b * dot_product(p, b) / norm(b); }

int main()
{
    int n=0;
    double x, y;
    xy_t P[110];
    while (~scanf("%lf,%lf", &x, &y))
    {
        P[n++] = xy_t(x, y);
    }
    double sum = 0.0;
    for (int i = 0; i + 2 < n; i++)
    {
        sum += cross_product(P[i + 1] - P[0], P[i + 2] - P[0]) / 2;
    }
    cout << abs(sum) << endl;
    return 0;
}