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;

double line(double a, double b, double c, double d){

  return sqrt(abs(a-c) * abs(a-c) + abs(b-d) * abs(b-d));

}

int main(){

  double x, y, xx, yy, xxx, yyy, s = 0, z, a, b, c;
  scanf("%lf,%lf", &x, &y);
  scanf("%lf,%lf", &xx, &yy);

  while(~scanf("%lf,%lf", &xxx, &yyy)){
    a = line(x, y, xx, yy);
    b = line(xx, yy, xxx, yyy);
    c = line(x, y, xxx, yyy);

    z = (a + b +c) / 2.0;

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

    xx = xxx, yy = yyy;
  }

  printf("%.12lf\n", s);
}