#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <complex>
using namespace std;

#define REP(i,n) for(int i=0;i<(int)n;++i)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();++i)
#define ALL(c) (c).begin(), (c).end()

const double EPS = 1e-8;
const double INF = 1e12;
typedef complex<double> P;
namespace std {
  bool operator < (const P& a, const P& b) {
    return real(a) != real(b) ? real(a) < real(b) : imag(a) < imag(b);
  }
}
double cross(const P& a, const P& b) {
  return imag(conj(a)*b);
}
double dot(const P& a, const P& b) {
  return real(conj(a)*b);
}

struct L : public vector<P> {
  L(const P &a, const P &b) {
    push_back(a); push_back(b);
  }
};

typedef vector<P> G;

struct C {
  P p; double r;
  C(const P &p, double r) : p(p), r(r) { }
};

int main() {
  double x,y;
  G g;
  while(scanf("%lf,%lf\n",&x,&y)==2)
    g.push_back(P(x,y));
  double ans = 0;
  REP(i, g.size()) {
    ans += cross(g[i],g[i<g.size()-1?i+1:0]);
  }
  printf("%.6lf\n",abs(ans / 2));
}