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<vector>
using namespace std;

typedef complex<double> xy_t;
vector <xy_t> v;

double heron(xy_t p1, xy_t p2, xy_t p3) {
    double a = abs(p2 - p1);
    double b = abs(p3 - p2);
    double c = abs(p1 - p3);
    double s = (a + b + c) / 2;
    return sqrt(s*(s - a)*(s - b)*(s - c));
}
int main()
{
    double x, y;
    char c;
    while (cin >> x >> c >> y) {
        complex<double> tmp(x, y);
        v.push_back(tmp);
    }
    double sum = 0;
    for (int i = 1; i < v.size() - 1; i++) {
        sum += heron(v[0], v[i], v[i + 1]);
    }
    cout << sum << endl;
    return 0;
}