题解 | #Freckles#

from math import sqrt

def dis(x,y):
    
    return sqrt((x[0]-y[0])**2+(x[1]-y[1])**2)


a=[]
dist=[]
res=0
c=input()
for i in range(int(c)):
    x,y = input().split()
    a.append([float(x),float(y)])

dist.append(a.pop())
while(len(a)!=0):
    
    dd=[]
    for i in a:
        for j in dist:     
            dd.append([dis(i,j),i,j])
    dd.sort()
    res+=dd[0][0]
    a.remove(dd[0][1])
    dist.append(dd[0][1])
print("%.2f" %res)