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>
#include <cstdio>

using namespace std;

int main(void){

  double x[1000];
  double y[1000];
  int i = 0;
  char ten;
  while( cin >> x[i] >> ten >> y[i] ){
    i++;
  }

  double S = 0;
  for( int j = 0 ; j < i ; j++ ){
    int J = j + 1;
    if( J == i ) J = 0;
    S =  S + x[J]*y[j] - x[j]*y[J];
  }
  S = abs(S)/2;
  printf("%.6f", S);
  cout << endl;
  return 0;
}