#include<iostream>




using namespace std;

double xa, xb, xc, ya, yb, yc;

int main()
{
	cin>>xa>>ya>>xb>>yb>>xc>>yc;
	cout<<sqrt(((xb-xa)*(xb-xa)+(yb-ya)*(yb-ya))*((xc-xa)*(xc-xa)+(yc-ya)*(yc-ya)))/2;
	return 0;
}