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<map>
#include<string>
#include<vector>
#include<algorithm>
#include<numeric>
#include<cmath>
using namespace std;

int main(){

  double x1, y1, x2, y2, x3, y3;
  scanf("%lf,%lf", &x1, &y1);
  scanf("%lf,%lf", &x2, &y2);
  double sum = 0.0;
  while( scanf("%lf,%lf", &x3, &y3) != EOF ){
    double a = sqrt( (x1-x2)*(x1-x2) + (y1-y2)*(y1-y2) );
    double b = sqrt( (x2-x3)*(x2-x3) + (y2-y3)*(y2-y3) );
    double c = sqrt( (x3-x1)*(x3-x1) + (y3-y1)*(y3-y1) );
    double z = a + b + c;
    z /= 2;
    sum += sqrt( z * (z-a) * (z-b) * (z-c) );
    // cerr << sum << endl;
    x2 = x3;
    y2 = y3;
  }
  printf("%.10lf\n", sum);

  return 0;
}