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 <cmath>
using namespace std;

double distance(double x1, double y1, double x2, double y2) {
  return sqrt((x1-x2) * (x1-x2) + (y1-y2) * (y1-y2));
}


int main() {
  int k=0;
  double x[20],y[20],xa,ya,S=0,a,b,c,z;
  while(scanf("%lf,%lf\n",&xa,&ya) == 2) {
    x[k] = xa;
    y[k] = ya;
    k++;
  }
  for(int i=0;i<k-2;i++) {
    a = distance(x[0],y[0],x[i+1],y[i+1]);
    b = distance(x[0],y[0],x[i+2],y[i+2]);
    c = distance(x[i+1],y[i+1],x[i+2],y[i+2]);
    z = (a + b + c) / 2;
    S += sqrt(z * (z - a) * (z - b) * (z - c));
  }
  printf("%.6lf\n",S);
}