#include<bits/stdc++.h>
using namespace std;
int main(){
	double a,b,c,d,e,f;
	while(cin >> a >> b >> c >> d >> e >> f){
		double S;
		S = fabs(a*(d-f)+c*(f-b)+e*(b-d))*0.5;
		cout << fixed <<setprecision(2) << S << endl;
	}	
	return 0;
}