x,y,xx,yy,xxx,yyy = map(int,input().split())
ans = 0
D = [(-1,0),(1,0),(0,-1),(0,1)]

for dx,dy in D:
  for dxx,dyy in D:
    for dxxx,dyyy in D:
      X,Y = x + dx,y + dy
      XX,YY = xx + dxx,yy + dyy
      XXX,YYY = xxx + dxxx,yyy + dyyy
      p,q,r,s = XX - X,YY - Y,XXX - X,YYY - Y
      ans = max(ans,abs(p*s - q*r))
print(ans / 2)