#pragma GCC optimize("O3")
#pragma GCC optimize(2)
#pragma GCC optimize(3)
#pragma GCC optimize("Ofast")
#pragma GCC optimize("inline")
#pragma GCC optimize("-fgcse")  
#pragma GCC optimize("-fgcse-lm")
#pragma GCC optimize("-fipa-sra")
#pragma GCC optimize("-ftree-pre")
#pragma GCC optimize("-ftree-vrp")
#pragma GCC optimize("-fpeephole2")
#pragma GCC optimize("-ffast-math")
#pragma GCC optimize("-fsched-spec")
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("-falign-jumps")   
#pragma GCC optimize("-falign-loops")
#pragma GCC optimize("-falign-labels")
#pragma GCC optimize("-fdevirtualize")
#pragma GCC optimize("-fcaller-saves")
#pragma GCC optimize("-fcrossjumping")
#pragma GCC optimize("-fthread-jumps")
#pragma GCC optimize("-funroll-loops")
#pragma GCC optimize("-freorder-blocks")
#pragma GCC optimize("-fschedule-insns")
#pragma GCC optimize("inline-functions")
#pragma GCC optimize("-ftree-tail-merge")
#pragma GCC optimize("-fschedule-insnS2")
#pragma GCC optimize("-fstrict-aliasing")
#pragma GCC optimize("-falign-functions")
#pragma GCC optimize("-fcse-follow-jumps")
#pragma GCC optimize("-fsched-interblock")
#pragma GCC optimize("-fpartial-inlining")
#pragma GCC optimize("no-stack-protector")
#pragma GCC optimize("-freorder-functions")
#pragma GCC optimize("-findirect-inlining")
#pragma GCC optimize("-fhoist-adjacent-loads")
#pragma GCC optimize("-frerun-cse-after-loop")
#pragma GCC optimize("inline-small-functions")
#pragma GCC optimize("-finline-small-functions")
#pragma GCC optimize("-ftree-switch-conversion")
#pragma GCC optimize("-foptimize-sibling-calls")
#pragma GCC optimize("-fexpensive-optimizations")
#pragma GCC optimize("inline-functions-called-once")
#pragma GCC optimize("-fdelete-null-Pointer-checks")
#pragma GCC optimize("Ofast")
 
#include <bits/stdc++.h>

using namespace std;

int x[3];
int y[3];
int res = 0;

int area(int x1,int y1,int x2,int y2,int x3,int y3)
{
    return abs(x1*y2 + x2*y3 + x3*y1 - x2*y1 - x3*y2 - x1*y3);
}
void dfs(int now)
{
    if(now==3)
    {
        res = max(res,area(x[0],y[0],x[1],y[1],x[2],y[2]));
        return;
    }
    x[now]-=1;
    dfs(now+1);
    x[now]+=2;
    dfs(now+1);
    x[now]-=1;
    y[now]-=1;
    dfs(now+1);
    y[now]+=2;
    dfs(now+1);
    y[now]-=1;
}
int main(void)
{
    cin.tie(0);
    ios::sync_with_stdio(false);

    cin >> x[0] >> y[0] >> x[1] >> y[1] >> x[2] >> y[2];

    dfs(0);

    if(res%2==0) cout << res/2 << ".0" << '\n';
    else cout << res/2 << ".5" << '\n';
    return 0;   
}