import std.stdio: readf, writeln;
import std.math.algebraic: sqrt;
import std.algorithm.comparison: max;

const dx = [0, 0, -1, 1];
const dy = [-1, 1, 0, 0];

void main() {
    int x1, y1, x2, y2, x3, y3;
    readf("%d %d %d %d %d %d\n", x1, y1, x2, y2, x3, y3);
    double res = 0;
    foreach(a; 0..4) {
        const p1 = x1 + dx[a];
        const q1 = y1 + dy[a];
        foreach(b; 0..4) {
            const p2 = x2 + dx[b];
            const q2 = y2 + dy[b];
            const x = sqrt(cast(double)(sqr(p1 - p2) + sqr(q1 - q2)));
            foreach(c; 0..4) {
                const p3 = x3 + dx[c];
                const q3 = y3 + dy[c];
                const y = sqrt(cast(double)(sqr(p2 - p3) + sqr(q2 - q3)));
                const z = sqrt(cast(double)(sqr(p3 - p1) + sqr(q3 - q1)));
                const s = (x + y + z) / 2;
                res = max(res, sqrt(s * (s - x) * (s - y) * (s - z)));
            }
        }
    }
    writeln(res);
}

pragma(inline)
long sqr(const long x) @safe @nogc { return x * x; }