#include<cmath>
#include<algorithm>
#include<iostream>
#include<vector>
#include<cstdio>

using namespace std;

double EPS = 1e-10;
const double PI = acos(-1);

double add(double a, double b){
  if(abs(a+b) < EPS * (abs(a)+abs(b)))return 0;
  return a+b;
}

struct point{
  double x, y;
  point(){}
  point(double x,double y) : x(x) , y(y){}

  point operator + (point p){
    return point(add(x,p.x), add(y,p.y));
  }

  point operator - (point p){
    return point(add(x,-p.x), add(y,-p.y));
  }

  point operator * (double d){
    return point(x*d,y*d);
  }

  point operator / (double d){
    return point(x/d,y/d);
  }
  
  bool operator == ( const point &p ) const {
    return fabs(x-p.x) < EPS && fabs(y-p.y) < EPS;
  }
};

struct segment{
  point a,b;
};

bool cmp_x(const point& p, const point& q){
  if(p.x != q.x)return p.x<q.x;
  return p.y < q.y;
}

double dot(point a, point b) {
  return (a.x * b.x + a.y * b.y);
}

double cross(point a, point b) {
  return (a.x * b.y - a.y * b.x);
}

double vec_abs(point a){
  return sqrt(a.x*a.x+a.y*a.y);
}

double dist(point a,point b){
  return sqrt(pow(a.x-b.x,2)+pow(a.y-b.y,2));
}

int ccw(point p0, point p1, point p2){
  point a = p1 - p0;
  point b = p2 - p0;
  if(cross(a,b)>EPS)return +1;
  if(cross(a,b)<EPS)return -1;
  if(dot(a,b)<-EPS)return +2;
  if(a.x*a.x+a.y*a.y<b.x*b.x+b.y*b.y)return -2;
  return 0;
}

vector<point>convex_hull(point* ps, int n){
  sort(ps,ps+n,cmp_x);
  int k=0;
  vector<point>qs(n*2);
  
  for(int i=0;i<n;i++){
    while(k>1&&cross(qs[k-1]-qs[k-2],ps[i]-qs[k-1])<0)k--;
    qs[k++]=ps[i];
  }
  
  for(int i=n-2,t=k;i>=0;i--){
    while(k>t&&cross(qs[k-1]-qs[k-2],ps[i]-qs[k-1])<0)k--;
    qs[k++]=ps[i];
  }
  qs.resize(k-1);
  return qs;
}

double areaPol(point* ps, int n){
  vector<point>t=convex_hull(ps,n);
  t.push_back(t[0]);
  int tsz=t.size();
  double area=0;
  for(int i=0;i<tsz-1;i++){
    area+=(t[i].x-t[i+1].x)*(t[i].y+t[i+1].y);
  }
  return abs(area)/2.0;
}


int main(void){
  point p[21];
  int n=0;
  double x,y;
  char k;

  while(cin>>x>>k>>y){
if(cin.eof())break;
    p[n].x = x;
    p[n].y = y;
    n++;
 }

  printf("%.6f\n",areaPol(p,n));

  return 0;
}