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

#define X first
#define Y second
typedef pair<double, double> Point;

double sq(double a) {return a*a;}

double gD(Point p1, Point p2) {
  return sqrt( sq(p1.X-p2.X)+sq(p1.Y-p2.Y) );
}

int main() {
  Point p[123456];
  char ch;
  int n=0;
  for(int i=0;cin>>p[i].X>>ch>>p[i].Y;i++) n++;
  double S=0;
  for(int i=1; i<n-1; i++) {
    double a=gD(p[0],p[i]), b=gD(p[i],p[i+1]), c=gD(p[i+1],p[0]);
    double z=(a+b+c)/2;
    S+=sqrt(z*(z-a)*(z-b)*(z-c));
  }
  printf("%.8f\n", S);
  
  return 0;
}