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;

typedef pair<double,double> dd;


double len(dd a, dd b){
  return sqrt(pow(a.first-b.first , 2)+pow(a.second-b.second,2));
}


int main(){

  vector < dd > dat(0);
  double x,y;
  double s=0,z;

  while(scanf("%lf,%lf",&x,&y)!=EOF){
    dat.push_back(dd(x,y));
  }

  for(int i=2; i<(int)dat.size(); i++){ 
    z = (len(dat[0],dat[i])+len(dat[i],dat[i-1])+len(dat[i-1],dat[0]) )/2.0;
    s += sqrt(z*(z-len(dat[0],dat[i]))*(z-len(dat[i],dat[i-1]))*(z-len(dat[i-1],dat[0])));
  }

  cout << s << endl;

  return 0;
}