#include <cstdio>
#include <algorithm>

using namespace std;

typedef long long ll;

struct pnt
{
  int x, y;

  pnt() {}
  pnt( int a, int b ) { x = a, y = b; }

  void read() { scanf("%d%d", &x, &y); }
};

pnt operator - ( pnt a, pnt b ) { return pnt(a.x - b.x, a.y - b.y); }
ll operator * ( pnt a, pnt b ) { return (ll)a.x * b.y - (ll)a.y * b.x; }

int main()
{
  pnt A, B, C;
  A.read();
  B.read();
  C.read();
  printf("%.1lf\n", 0.5 * abs((A - B) * (C - B)));
  return 0;
}