#include<bits/stdc++.h>
using namespace std;
int main(){
	double x1,y1,x2,y2,x3,y3;
	cin>>x1>>y1>>x2>>y2>>x3>>y3;
	cout<<fixed<<setprecision(2)<<sqrt(((abs(x1-x2)+abs(x1-x3)+abs(x2-x3))/2)*(((abs(x1-x2)+abs(x1-x3)+abs(x2-x3))/2)-abs(x1-x2))*(((abs(x1-x2)+abs(x1-x3)+abs(x2-x3))/2)-abs(x1-x3))*(((abs(x1-x2)+abs(x1-x3)+abs(x2-x3))/2)-abs(x2-x3)));
}