x1,y1,x2,y2,x3,y3=map(float,input().split()) a=x2-x1 b=y2-y1 c=x3-x1 d=y3-y1 q=pow(aa+ab,0.5) w=pow(cc+dd,0.5) cos=(ac+bd)/(q+w) sin=pow(1-cos,0.5) s=1/2qw*sin s=float(s) print("%0.2f"%s)