//include
//------------------------------------------
#include <vector>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <fstream>
#include <complex>
#include <math.h>

using namespace std;

//conversion
//------------------------------------------
inline long toLong(string s) {long v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}

//math
//-------------------------------------------
template<class T> inline T sqr(T x) {return x*x;}

//typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef pair<long, long> PLL;
typedef long long LL;
//container util
//------------------------------------------
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())

//repetition
//------------------------------------------
#define FOR(i,a,b) for(long i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)

//constant
//--------------------------------------------

//clear memory
#define CLR(a) memset((a), 0 ,sizeof(a))

const long double EPS = 1e-18;
const double INF = 1e9;



int main(){
	long double x,y,xsum=0.0,ysum=0.0;
	char c;
	int cnt=0;
	vector<pair<long double,long double> >pi;
	while(cin>>x>>c>>y){
		pi.PB(MP(x,y));
		xsum+=x;ysum+=y;
		cnt++;
	}
	long double cx=xsum/cnt,cy=ysum/cnt;
	pi.PB(pi[0]);
	long double res=0.0;
	REP(i,SZ(pi)-1){
		long double a=sqrt(abs(cx-pi[i].first)*abs(cx-pi[i].first)+abs(cy-pi[i].second)*abs(cy-pi[i].second));
		long double b=sqrt(abs(cx-pi[i+1].first)*abs(cx-pi[i+1].first)+abs(cy-pi[i+1].second)*abs(cy-pi[i+1].second));
		long double c=sqrt(abs(pi[i].first-pi[i+1].first)*abs(pi[i].first-pi[i+1].first)+abs(pi[i].second-pi[i+1].second)*abs(pi[i].second-pi[i+1].second));
		long double z=(a+b+c)/2.0;
		res+=sqrt(z*(z-a)*(z-b)*(z-c));
		//cout<<fixed<<setprecision(7)<<sqrt(z*(z-a)*(z-b)*(z-c))<<endl;
		
	}
	cout<<fixed<<setprecision(7)<<res<<endl;
	return 0;
}