import numpy as np

def dist(ax, ay, bx, by):

  ans = np.sqrt( (ax-bx)**2 +(ay-by)**2 )

  return ans



N = int(eval(input()))

xs = []

ys = []



for _ in range(N):

  x, y = list(map(int, input().split()))

  xs.append(x)

  ys.append(y)



di2 = 0.0

for i in range(N):

  for j in range(N):

    if i >= j:

      continue

    else:

      di2 += dist(xs[i], ys[i], xs[j], ys[j])



print((2.0*di2/N))
def dist(a, b):

  return ( (a[0]-b[0])**2 + (a[1]-b[1])**2 )**0.5



N = int(eval(input()))

xy = []



for _ in range(N):

  x, y = list(map(int, input().split()))

  xy.append([x,y])



di2 = 0.0

for i in range(N):

  for j in range(N):

    if i >= j:

      continue

    else:

      di2 += dist(xy[i], xy[j])



print((2.0*di2/N))
import numpy as np


def dist(ax, ay, bx, by):
    ans = np.sqrt((ax - bx) ** 2 + (ay - by) ** 2)
    return ans


N = int(eval(input()))
xs = []
ys = []
for _ in range(N):
    x, y = list(map(int, input().split()))
    xs.append(x)
    ys.append(y)
di2 = 0.0
for i in range(N):
    for j in range(N):
        if i >= j:
            continue
        else:
            di2 += dist(xs[i], ys[i], xs[j], ys[j])
print((2.0 * di2 / N))

def dist(a, b):
    return ((a[0] - b[0]) ** 2 + (a[1] - b[1]) ** 2) ** 0.5


N = int(eval(input()))
xy = []
for _ in range(N):
    x, y = list(map(int, input().split()))
    xy.append([x, y])
di2 = 0.0
for i in range(N):
    for j in range(N):
        if i >= j:
            continue
        else:
            di2 += dist(xy[i], xy[j])
print((2.0 * di2 / N))

-import numpy as np - - -def dist(ax, ay, bx, by): -    ans = np.sqrt((ax - bx) ** 2 + (ay - by) ** 2) -    return ans +def dist(a, b): +    return ((a[0] - b[0]) ** 2 + (a[1] - b[1]) ** 2) ** 0.5 -xs = [] -ys = [] +xy = [] -    xs.append(x) -    ys.append(y) +    xy.append([x, y]) -            di2 += dist(xs[i], ys[i], xs[j], ys[j]) +            di2 += dist(xy[i], xy[j])