/* -*- coding: utf-8 -*-
 *
 * 2790.cc:  No.2790 Athena 3 - yukicoder
 */

#include<cstdio>
#include<algorithm>
 
using namespace std;

/* constant */

const int K = 3;
const int dxs[] = { 1, 0, -1, 0 }, dys[] = { 0, -1, 0, 1 };

/* typedef */

/* global variables */

int xs[K], ys[K];

/* subroutines */

inline int area(int vx0, int vy0, int vx1, int vy1) {
  return abs(vx0 * vy1 - vx1 * vy0);
}

/* main */

int main() {
  for (int i = 0; i < K; i++) scanf("%d%d", xs + i, ys + i);

  int maxa = 0, kbits = 1 << (K * 2);
  for (int bits = 0; bits < kbits; bits++) {
    int dis[K], cxs[K], cys[K];
    for (int i = 0; i < K; i++) {
      int di = (bits >> (i * 2)) & 3;
      cxs[i] = xs[i] + dxs[di], cys[i] = ys[i] + dys[di];
    }

    int a = area(cxs[1] - cxs[0], cys[1] - cys[0],
		 cxs[2] - cxs[0], cys[2] - cys[0]);
    maxa = max(maxa, a);
  }

  printf("%.1lf\n", 0.5 * maxa);
  
  return 0;
}