#include <cstdio>
#include <iostream>
#include <cmath>
#include <cstdlib>
using namespace std;
struct P{
	double x,y;
};
P p[100];
double sqr(int n){
	return n * n;
}
double func(int i){
	double a = sqrt(sqr(p[0].x - p[i-1].x)+sqr(p[0].y - p[i-1].y));
	double b = sqrt(sqr(p[0].x - p[i].x)+sqr(p[0].y - p[i].y));
	double c = sqrt(sqr(p[i].x - p[i-1].x)+sqr(p[i].y - p[i-1].y));
	double z = a + b + c;
	return sqrt((z/2)*((z/2)-a)*((z/2)-b)*((z/2)-c));
}
int main(){
	double x,y;
	int cnt = 0;
	while(~scanf("%lf,%lf",&p[cnt].x,&p[cnt].y)){
		cnt++;
	}
	double ans = 0;
	for(int i = 2; i < cnt; i++){
		ans += func(i);
	}
	printf("%.6lf\n",ans);
}