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>

#define MAX 21
 
double dis(double x1, double y1, double x2, double y2)
{
    double d;
    d = sqrt(pow(x2 - x1, 2) + pow(y2 - y1, 2));
    return d;
}
 
int main()
{
    double x[MAX], y[MAX];
    int t = 0;
    double S = 0.0, z, a, b, c;
 
    while (1) {
	if(scanf("%lf,%lf",&x[t] ,&y[t]) == EOF) break;
	t++;
    }
 
    for (int i = 2; i < t; i++) {
	a = dis(x[0], y[0], x[i-1], y[i-1]);
	b = dis(x[0], y[0], x[i], y[i]);
	c = dis(x[i-1], y[i-1], x[i], y[i]);
	z = (a + b + c) / 2;
 
	S += sqrt(z * (z - a) * (z - b) * (z - c));
    }
    printf("%.6f\n", S);
    return 0;
}