#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define rep(i,a,b) for(it i=(it)(a);i<=(it)b;i++)
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define moda 998244353LL
#define modb 1000000007LL
#define dai 2500000000000000000LL
#define tyu 2500000000
#define sho -dai
#define eps 1e-14
#define yn(x) cout<<(x ? "Yes":"No")<<endl;
#define YN(x) cout<<(x ? "YES":"NO")<<endl;
using it=long long;
using ll=long long;
using un=unsigned long long;
using db=long double;
using st=string;
using ch=char;
using bo=bool;
using P=pair<it,it>;
using T=tuple<it,it,it>;
using mint=modint;
using vi=vector<it>;
using vd=vector<db>;
using vs=vector<st>;
using vc=vector<ch>;
using vb=vector<bo>;
using vp=vector<P>;
using vm=vector<mint>;
using sp=set<P>;
using ss=set<st>;
using si=set<it>;
using vvi=vector<vi>;
using vvd=vector<vd>;
using vvs=vector<vs>;
using vvb=vector<vb>;
using vvc=vector<vc>;
using vvp=vector<vp>;
using vvm=vector<vm>;
using vsi=vector<si>;
using vsp=vector<sp>;
using vvsi=vector<vsi>;
using vvsp=vector<vsp>;
using vvvi=vector<vvi>;
using vvvd=vector<vvd>;
using vvvvi=vector<vvvi>;
const it dx[4]={0,1,0,-1};
const it dy[4]={1,0,-1,0};

db san(db x_a,db y_a,db x_b,db y_b,db x_c,db y_c){
  x_b-=x_a;
  y_b-=y_a;
  x_c-=x_a;
  y_c-=y_a;
  return abs(x_b*y_c-y_b*x_c);
}

int main(){
  db a,b,c,d,e,f;cin>>a>>b>>c>>d>>e>>f;
  db ans=0;
  rep(i,-1,1)
    rep(j,-1,1){
      if(!(i+j==i||i+j==j))continue;
      rep(k,-1,1)
        rep(l,-1,1){
          if(!(k+l==k||k+l==l))continue;
          rep(m,-1,1)
            rep(n,-1,1){
              if(!(m+n==m||m+n==n))continue;
              ans=max(ans,san(a+i,b+j,c+k,d+l,e+m,f+n));
            }
      }
    }
  cout<<fixed<<setprecision(2);
  cout<<ans/2<<endl;
}