from math import sqrt
def dis(l):
return sqrt(((l[0] - l[2])**2) + ((l[1] -l[3])**2))
def getR(a,b,c):
s = (a + b + c)/2
R = (a*b*c)/(4*((s*(s-a)*(s-b)*(s-c))**(1/2)))
return R
while True:
try:
L = list(map(float,input().split()))
except:
break
a,b,c = sorted([dis(L[0:4]), dis(L[2:]), dis(L[4:]+L[:2])])
print("%.2f" % (getR(a,b,c)*2*3.141592653589793))