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<cmath>
#include<algorithm>
#include<iostream>
#include<vector>
#include<cstdio>

using namespace std;

struct point{double x, y;};

double areaPol(vector<point> t){
  t.push_back(t[0]);
  int tsz=t.size();
  double area=0;
  for(int i=0;i<tsz-1;i++){
    area+=(t[i].x-t[i+1].x)*(t[i].y+t[i+1].y);
  }
  return abs(area)/2.0;
}

int main(void){
  point p;
  vector<point>t;
  char k;

  while(cin>> p.x >> k >> p.y)t.push_back(p);

  printf("%.6f\n",areaPol(t));

  return 0;
}