#include <iostream>
#include <cmath>
using namespace std;
double rast(double x1, double y1, double x2, double y2) {
    return sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
}
int main() {
    double x1, y1, x2, y2, x3, y3, a, b, c, p = 0, ans;
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    a = rast(x1, y1, x2, y2);
    b = rast(x2, y2, x3, y3);
    c = rast(x1, y1, x3, y3);
    p = (a + b + c) / 2;
    ans = sqrt(p * (p - a) * (p - b) * (p - c));
    printf("%.1f", ans);
}