#include <iostream>
#include <cmath>

using namespace std;

int main() {
  long long x1, y1, x2, y2, x3, y3; cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
  long long abx = x2 - x1;
  long long aby = y2 - y1;
  long long acx = x3 - x1;
  long long acy = y3 - y1;
  long long S = abs(abx * acy - aby * acx);
  cout << S / 2;
  if (S % 2 != 0) cout << ".5";
  return 0;
}