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 <bits/stdc++.h>
using namespace std;
double len(double, double, double, double);

int main() {
  double x, y, lx, ly, s = 0.0, sx, sy;
  char c;
  cin >> lx >> c >> ly;
  sx = lx;
  sy = ly;
  while(cin >> x >> c >> y) {
    double a = len(sy, sx, ly, lx);
    double b = len(sy, sx, y, x);
    double c = len(ly, lx, y, x);
    double z = (a + b + c) / 2.0;
    double bu = z * (z - a) * (z - b) * (z - c);
    s += pow(bu, 1.0 / 2.0);
    lx = x;
    ly = y;
  }
  cout << s << endl;
  return 0;
}

double len(double sy, double sx, double ey, double ex) {
  double y = ey - sy;
  double x = ex - sx;
  return pow(pow(y, 2) + pow(x, 2), 1.0 / 2.0);
}