// Problem: No.2790 Athena 3
// Group: yukicoder
// URL: https://yukicoder.me/problems/no/2790
// Memory Limit: 512 MB
// Time Limit: 2000 ms
// Author: lingfunny
// 
// Powered by CP Editor (https://cpeditor.org)

#include <bits/stdc++.h>
using namespace std;

const int dx[] = { 0, 0, 1, -1 };
const int dy[] = { 1, -1, 0, 0 };
int x[3], y[3], ans;

int calc() {
	int x1 = x[1] - x[0], x2 = x[2] - x[0];
	int y1 = y[1] - y[0], y2 = y[2] - y[0];
	return abs(y2 * x1 - y1 * x2);
}

void dfs(int i) {
	if (i >= 3) {
		ans = max(ans, calc());
		return;
	}
	for (int d = 0; d < 4; ++d) {
		x[i] += dx[d], y[i] += dy[d];
		dfs(i + 1);
		x[i] -= dx[d], y[i] -= dy[d];
	}
}


int main() {
	for (int i = 0; i <= 2; ++i)
		scanf("%d%d", x + i, y + i);
	dfs(0);
	printf("%.1lf\n", ans * 0.5);
	return 0;
}