#include <iostream>
#include <iomanip>
#include <sstream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
#include <climits>
#include <cfloat>
#include <string>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <bitset>
#include <algorithm>
#include <functional>
#include <utility>
#include <numeric>

using namespace std;

typedef unsigned int UI;
typedef long long LL;
typedef unsigned long long ULL;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int,int> PII;
typedef istringstream ISS;
typedef ostringstream OSS;

#define REP( i, m, n ) for ( int i = (int)( m ); i < (int)( n ); ++i )
#define EACH( v, c ) for ( auto &v : c )

#define ITER( c ) __typeof( (c).begin() )
#define IREP( c, it ) for ( ITER(c) it = c.begin(); it != c.end(); ++it )
#define ALL( c ) (c).begin(), (c).end()

#define PB( n ) push_back( n )
#define MP( a, b ) make_pair( ( a ), ( b ) )
#define EXIST( c, e ) ( (c).find( e ) != (c).end() )

#define fst first
#define snd second

#define DUMP( x ) cerr << #x << " = " << ( x ) << endl
#define DEBUG( x ) cerr << __FILE__ << ":" << __LINE__ << ": " << #x << " = " << ( x ) << endl

struct Point
{
	double x, y;

	Point() : x( 0 ), y( 0 )
	{
		return;
	}

	Point( double x, double y ) : x( x ), y( y )
	{
		return;
	}

	Point operator + ( const Point &a ) const
	{
		return Point( x + a.x, y + a.y );
	}

	Point operator - ( const Point &a ) const	{
		return Point( x + ( -a.x ), y + ( -a.y ) );
	}

	Point operator * ( const double &a ) const
	{
		return Point( x * a, y * a );
	}

	Point operator / ( const double &a ) const
	{
		return Point( x / a, y / a );
	}

	bool operator < ( const Point &a ) const
	{
		return x == a.x ? y < a.y : x < a.x;
	}
};

double distance( const Point &a, const Point &b )
{
	return sqrt( pow( a.x - b.x, 2. ) + pow( a.y - b.y, 2. ) );
}

int main()
{
	cin.tie( 0 );
	ios::sync_with_stdio( false );

	double x, y;
	char d;

	vector< Point > ps;

	while ( cin >> x >> d >> y )
	{
		ps.PB( Point( x, y ) );
	}

	const int N = ps.size();

	double res = 0;

	REP( i, 1, N )
	{
		double a = distance( ps[0], ps[i] );
		double b = distance( ps[0], ps[ i + 1 ] );
		double c = distance( ps[ i ], ps[ i + 1 ] );
		double z = ( a + b + c ) / 2;

		res += sqrt( z * ( z - a ) * ( z - b ) * ( z - c ) );
	}

	cout.precision( 7 );
	cout << fixed;

	cout << res << endl;

	return 0;
}