import math
n=int(input())
lst=[]
for i in range(n):
    set1=tuple(map(int,input().split()))
    lst.append(set1)
lst.sort(key=lambda x:x[1])
long=0
for i in range(n-1):
    long+=math.sqrt((lst[i+1][0]-lst[i][0])**2+(lst[i+1][1]-lst[i][1])**2+(lst[i+1][2]-lst[i][2])**2)
print(f'{long:.3f}')