#include <iostream>
#include <iomanip>
#include <cassert>
#include <algorithm>
#include <functional>
#include <vector>
#include <string>
#include <cstring>
#include <stack>
#include <queue>
#include <map>
#include <bitset>
#include <sstream>
#include <istream>
#include <cmath>
#include <cstdio>

using namespace std;

#define vci vector<int>
#define vcs vector<string>
#define pb push_back
#define sz size()
#define mapii map<int, int>
#define mapci map<char, int>
#define mapsi map<string, int>
#define all(x) x.begin(), x.end()
#define minit(a, i) memset(a, i, sizeof(a));

#define for_(i, a, b) for (int i=(int)a; i<(int)b; i++)
#define for_d(i, a, b) for (int i=(int)a-1; i>=b; i--)
#define for_r(i, a, b, c) for (int i=(int)a; i<(int)b; i += c)
#define for_dr(i, a, b, c) for (int i=(int)a-1; i>=b; i -= c)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();++i)

template <class T> int __builtin_popcount(T n) { return n ? 1 + __builtin_popcount(n & (n - 1)) : 0; }

typedef long long ll;
typedef double D;

const int iINF = 2147483647;
const ll lINF = 9223372036854775807;

template <class T> inline void dbg(T t) { cout << t << endl; }




// define eps
double EPS = 1e-10;

// Point2D & Vector2D
struct Point2D { 
	double x, y;
	Point2D (double a=0, double b=0) : x(a), y(b) {}
};
typedef Point2D Vector2D;

// Point2D's and Vector2D's operator
Point2D operator + (Point2D a, Point2D b) { return Point2D(a.x + b.x, a.y + b.y); }
Point2D operator - (Point2D a, Point2D b) { return Point2D(a.x - b.x, a.y - b.y); }
Point2D operator * (Point2D a, double d) { return Point2D(a.x * d, a.y * d); }
Point2D operator / (Point2D a, double d) { return Point2D(a.x / d, a.y / d); }

bool operator < (const Point2D& a, const Point2D& b) { return a.x != b.x ? a.x < b.x : a.y < b.y; }
bool operator > (const Point2D& a, const Point2D& b) { return b.x != a.x ? b.x < a.x : b.y < a.y; }
bool operator == (const Point2D& a, const Point2D& b) { return fabs(a.x-b.x)<EPS && fabs(a.y-b.y)<EPS; }

// basic function
double norm(Point2D a) { return a.x*a.x + a.y*a.y; }
double dot2D(const Vector2D& a, const Vector2D& b) { return a.x * b.x + a.y * b.y; }
double cross2D(const Vector2D& a, const Vector2D& b) { return a.x*b.y - a.y*b.x; }
double dist2D(const Point2D& a, const Point2D& b) { return sqrt( (a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y) ); }



bool end(vector<bool>& use, int n) {
	int cntf = 0;
	for_(i, 0, n) if (!use[i]) cntf++;
	return cntf==2;
}

int far(Point2D cent, vector<Point2D>& points, vector<bool>& use, int n) {
	int bfar = 0, ret = -1;
	for_(i, 0, n) {
		if (use[i]) continue;
		int dist = dist2D(cent, points[i]);
		if (bfar < dist) {
			bfar = dist;
			ret = i;
		}
	}
	return ret;
}

D calc(D a, D b, D c) {
	D z = (a+b+c)/2.0;
	return sqrt( z*(z-a)*(z-b)*(z-c) );
}

int main() {
	vector<Point2D> points;
	vector<bool> use(30, 0);
	
	D x, y; char c;
	while (cin>>x>>c>>y) {
		Point2D p(x, y);
		points.pb(p);
	}
	
	D ans = 0;
	int n = (int)points.sz;
	while (!end(use, n)) {
		Point2D cent(0, 0);
		int med = far(cent, points, use, n);
		
		int prev = (med-1+n)%n, next = (med+1)%n;
		while (use[prev]) { prev = (prev-1+n)%n; }
		while (use[next]) { next = (next+1)%n; }
		
		D a = dist2D(points[med],points[prev]);
		D b = dist2D(points[med], points[next]);
		D c = dist2D(points[prev], points[next]);
		
		D S_ = calc(a, b, c);
		ans += S_;
		
		use[med] = 1;
	}
	
	cout << ans << endl;
	
	return 0;
}

Measured memory_bytes: 1292