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.

<image>



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 <cstdio>
#include <cmath>
using namespace std;

int main()
{
    double x1, y1, x2, y2, x3, y3;
    scanf("%lf,%lf %lf,%lf", &x1, &y1, &x2, &y2);
    double ans = 0.0;
    
    while(scanf("%lf,%lf", &x3, &y3) != EOF){
        double a = sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1- y2)); 
        double b = sqrt((x2 - x3) * (x2 - x3) + (y2 - y3) * (y2- y3));
        double c = sqrt((x3 - x1) * (x3 - x1) + (y3 - y1) * (y3- y1));
        double z = (a + b + c) / 2;
        ans += sqrt(z * (z - a) * (z - b) * (z - c));
        x2 = x3; y2 = y3;
    }
    
    printf("%.7f\n", ans);
}