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 <cstdio>
#include <algorithm>
#include <complex>
#include <vector>
#include <cmath>
using namespace std;
typedef complex<double> P;

double cross(P a, P b) {
  return a.real()*b.imag() - a.imag()*b.real();
}

int main() {
  vector<P> g;
  double x, y;
  while(scanf("%lf,%lf", &x, &y) != EOF) {
    g.push_back(P(x,y));
  }
  int N = g.size();
  double S = 0;
  for(int i = 0; i < N; ++i) {
    S += cross(g[i], g[(i+1)%N]);
  }
  printf("%.10f\n", abs(S)/2.0);
  return 0;
}