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<cstdio>
#include<vector>
#include<cmath>
using namespace std;
typedef pair<double,double> P;
double cross(P p1,P p2){
  return p1.first*p2.second-p1.second*p2.first;
}
double getArea(vector<P> p){
  double sum=0;
  for(int i=0;i<p.size();i++)sum+=cross(p[i],p[(i+1)%p.size()]);
  return abs(sum/2.0);
}

int main(){
  vector<P> poly;
  P p;
  while(scanf("%lf,%lf",&p.first,&p.second) != EOF){
    poly.push_back(p);
  }
  printf("%.6f\n",getArea(poly));
}