#include <bits/stdc++.h>
using namespace std;
void _main();
int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	_main();
	return 0;
}
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using vi = std::vector<int>;
using vvi = std::vector<vi>;
using vl = std::vector<ll>;
using vii = std::vector<pair<int, int> >;
using vvl = std::vector<vl>;
using vll = std::vector<pair<ll , ll> >;
using vd = std::vector<double>;
using vvd = std::vector<vd>;
using vs = std::vector<std::string>;
using vvs = std::vector<vs>;
using vb = std::vector<bool>;
using vvb = std::vector<vb>;
using vc = std::vector<char>;
using vvc = std::vector<vc>;
using pii = std::pair<int, int>;
using pll = std::pair<ll, ll>;
using piil = std::pair<pair<int, int>, ll>;
using mii = std::map<int, int>;
using mll = std::map<ll, ll>;
using pql = std::priority_queue<ll>;
using pqi = std::priority_queue<int>;
using pqiil = std::priority_queue<pair<pair<int, int>, ll> >;
using pqii = std::priority_queue<pair<int, int> >;

#define pb push_back
#define ps push
#define eb emplace_back
#define is insert
#define er erase
#define f first
#define s second
#define lb lower_bound
#define ub upper_bound
#define sf(i) sizeof(i)
#define endl "\n"
#define sz(v) ((int)(v).size())
#define all(v) (v).begin(), (v).end()
#define rep(i, L, R) for(ll i = L;i<=R;i++)
#define pcis precision

template<typename T>
struct infinity {
	static constexpr T max=std::numeric_limits<T>::max();
	static constexpr T min=std::numeric_limits<T>::min();
	static constexpr T value=std::numeric_limits<T>::max()/2;
	static constexpr T mvalue=std::numeric_limits<T>::min()/2;
};
template<typename T>constexpr T INF=infinity<T>::value;
constexpr ll lINF=INF<ll>;
constexpr int iINF = INF<int>;
constexpr ld PI = 3.1415926535897932384626;

ll get(ll A,ll  B, ll C, ll D, ll E, ll F) {
	return abs(A*D+C*F+E*B-B*C-D*E-F*A);
}

ll dx[4] = {0, -1, 0, 1};
ll dy[4] = {-1, 0, 1, 0};

void _main() {

	ll A, B, C, D, E, F;
	cin >>A>>B>>C>>D>>E>>F;

	ll MX = 0;
	ll K[4] = {0,1,2,3};
	for (auto i : K) {
		for (auto j : K) {
			for (auto k : K) {
				MX = max(MX, get(A+dx[i], B+dy[i], C+dx[j], D+dy[j], E+dx[k], F+dy[k]));
			}
		}
	}
	
	if (MX&1) {
		cout << MX/2;
		cout << ".5" << endl;
	}else {
		cout << MX/2;
		cout << ".0" << endl;
	}







}