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 <cmath>
using namespace std;

int main() {
    double x[3], y[3], sum = 0;
    scanf("%lf,%lf", &x[0], &y[0]);
    scanf("%lf,%lf", &x[1], &y[1]);
    while (scanf("%lf,%lf", &x[2], &y[2]) != EOF) {
        double side[3];
        for (int i = 0; i < 3; i++) {
            side[i] = sqrt(pow(x[i] - x[(i + 1) % 3], 2) + pow(y[i] - y[(i + 1) % 3], 2));
        }
        double z = (side[0] + side[1] + side[2]) / 2;
        sum += sqrt(z * (z - side[0]) * (z - side[1]) * (z - side[2]));
        x[1] = x[2];
        y[1] = y[2];
    }
    printf("%.6f\n", sum);
}