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>

#define REP(i,n) for(int i=0;i<(int)n;++i)

using namespace std;

using ld = long double;
using P = complex<ld>;
using VP = vector<P>;

ld cross (P a, P b) { return imag(conj(a) * b); }

ld area(const VP &p) {
  ld res = 0;
  int n = p.size();
  REP(j,n) res += cross(p[j], p[(j+1)%n]);
  return abs(res / 2);
}

int main() {
  VP vp;
  double x, y;
  while(scanf("%lf,%lf\n", &x, &y) != EOF) {
    vp.emplace_back(x, y);
  }
  cout << setprecision(10) << fixed << area(vp) << endl;
  return 0;
}