#include <iostream>
#include <cstdio>
#include <iomanip> // setprecision
#include <complex>
#include <cmath>
using namespace std;

typedef complex<double> point;

double inner_product(point x, point y) {
  return (conj(x) * y).real();
}

double outer_product(point x, point y) {
  return (conj(x) * y).imag();
}

point normalize(point a) {
  return a * (1/abs(a)); // normはabsの2乗、absは本来のノルム。
}

point projection(point a, point b) {
  point e = normalize(b);
  return e * inner_product(a, e);
}

int main() {
  point P[30];
  double x, y;
  int n = 0;
  while (scanf("%lf,%lf", &x, &y) != EOF) {
    P[n++] = point(x, y);
  }
  double S = 0;
  for (int i=0; i<n-1; i++) {
    S += outer_product(P[i], P[i+1])/2;
  }
  cout << fixed << setprecision(10) << abs(S) << endl;
}