import std.stdio,std.string,std.conv,std.math;

int main()
{
	int count = 0;
	double ans = 0;
	double x[25];
	double y[25];
	string s;
	while((s = readln.chomp).length != 0)
	{
		string[] _s = s.split(",");
		x[count] = _s[0].to!double;
		y[count] = _s[1].to!double;
	}

	x[count] = x[0];
	y[count] = y[0];

	foreach(i;0..count)
	{
		ans += x[i]*y[i+1] - x[i+1]*y[i];
	}

	writeln(abs(ans)/2);
	return 0;
}