x1,y1,x2,y2,x3,y3=map(int,input().split()) ab=((x1-x2)**2+(y1-y2)**2)**0.5 ac=((x1-x3)**2+(y1-y3)**2)**0.5 bc=((x2-x3)**2+(y2-y3)**2)0.5 p=0.5(ab+ac+bc) s=(p(p-ab)(p-ac)(p-bc))**0.5 print('%.2f'%s)