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 <bits/stdc++.h>

using namespace std;

struct P {
    double x, y;
    bool operator<(const P &r) const {
        return x < r.x;
    }
};

int main() {

    int n;
    char split;
    double a, b, c, x, y, z, s = 0;
    P p[20];

    for(n = 0; cin >> x >> split >> y; ++n) {

        p[n].x = x;
        p[n].y = y;

    }

    for(int i = 0; i < n - 2; ++i) {

        a = hypot(p[0].x - p[i + 1].x, p[0].y - p[i + 1].y);
        b = hypot(p[0].x - p[i + 2].x, p[0].y - p[i + 2].y);
        c = hypot(p[i + 1].x - p[i + 2].x, p[i + 1].y - p[i + 2].y);

        z = (a + b + c) / 2;

        s += sqrt(z * (z - a) * (z - b) * (z - c));

    }

    printf("%.6f\n", s);

}