import sys
import math

data = sys.stdin.read().split()
n = int(data[0])
xs = []
ys = []
idx = 1
for _ in range(n):
    xs.append(int(data[idx]))
    ys.append(int(data[idx+1]))
    idx += 2
min_e = [float('inf')] * n
used = [False] * n
min_e[0] = 0.0
ans = 0.0
for _ in range(n):
    v = -1
    for i in range(n):
        if not used[i] and (v == -1 or min_e[i] < min_e[v]):
            v = i
    used[v] = True
    ans += math.sqrt(min_e[v])
    vx, vy = xs[v], ys[v]
    for u in range(n):
        if not used[u]:
            dist_sq = (xs[u] - vx)**2 + (ys[u] - vy)**2
            if dist_sq < min_e[u]:
                min_e[u] = dist_sq
print(f"{ans:.10f}")