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

int main() {
  double x1, y1, x2, y2, x3, y3;
  double a, b, c, z, s = 0.0;
  scanf("%lf,%lf\n", &x1, &y1);
  scanf("%lf,%lf\n", &x2, &y2);
  while (scanf("%lf,%lf\n", &x3, &y3) == 2) {
    a = sqrt((x2-x1)*(x2-x1) + (y2-y1)*(y2-y1));
    b = sqrt((x3-x1)*(x3-x1) + (y3-y1)*(y3-y1));
    c = sqrt((x3-x2)*(x3-x2) + (y3-y2)*(y3-y2));
    z = (a+b+c)*0.5;
    s += sqrt(z*(z-a)*(z-b)*(z-c));
    x2 = x3;
    y2 = y3;
  }
  printf("%.6lf\n", s);
  return 0;
}