from math import sqrt
num = int(input())
point = []
for i in range(num):
    point.append(input().split())

point = sorted(point,key = lambda alpha: alpha[2])
total = 0
p = []
for i in point:
    i = [int(j) for j in i]
    p.append(i)

point = p[:]

for i in range(len(point)-1):
    total+=sqrt((point[i+1][0]-point[i][0])**2+(point[i+1][1]-point[i][1])**2+(point[i+1][2]-point[i][2])**2) 

print('%.3f' %total)