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 <complex.h>
#include <cmath>
#include <iostream>
#include <vector>
#include <stdio.h>

using namespace std;

typedef complex<double> xy_t;

double dot_product(xy_t a, xy_t b) {
  return (conj(a)*b).real();
}

double cross_product(xy_t a, xy_t b) {
  return (conj(a)*b).imag();
}

int main() {
  xy_t P[110];
  int N = 0;
  double x, y;
  
  while(scanf("%lf,%lf", &x, &y)!= EOF) {
    xy_t entry(x,y);
    P[N++] = entry;
  }

  //center all coordinates based on first element
  for (int i = 1; i < N; i++) {
    P[i] -= P[0];
  }
  
  //calculate sum
  double sum = 0.0;
  for (int i = 1; i+1 < N ; i++) {
    xy_t  a = P[i] , b = P[i + 1];
    sum += cross_product(a, b) / 2.0;
  }

  printf("%.6f\n", abs(sum));
  
}