def c_average_length():

    from itertools import permutations

    from math import factorial

    N = int(eval(input()))

    Positions = [[int(i) for i in input().split()] for j in range(N)]



    ans = 0.0

    for route in permutations(list(range(N)), N):

        tmp = 0.0

        for i in range(N - 1):

            cur_v = route[i]

            next_v = route[i + 1]

            tmp += ((Positions[next_v][0] - Positions[cur_v][0])**2 +

                    (Positions[next_v][1] - Positions[cur_v][1])**2)**0.5

        ans += tmp

    return ans / factorial(N)



print((c_average_length()))
def c_average_length():

    N = int(eval(input()))

    Positions = [[int(i) for i in input().split()] for j in range(N)]



    ans = 0.0

    for i in range(N):

        for j in range(i + 1, N):

            ans += ((Positions[i][0] - Positions[j][0])**2 +

                    (Positions[i][1] - Positions[j][1])**2)**0.5

    return ans * 2 / N



print((c_average_length()))
def c_average_length():
    from itertools import permutations
    from math import factorial

    N = int(eval(input()))
    Positions = [[int(i) for i in input().split()] for j in range(N)]
    ans = 0.0
    for route in permutations(list(range(N)), N):
        tmp = 0.0
        for i in range(N - 1):
            cur_v = route[i]
            next_v = route[i + 1]
            tmp += (
                (Positions[next_v][0] - Positions[cur_v][0]) ** 2
                + (Positions[next_v][1] - Positions[cur_v][1]) ** 2
            ) ** 0.5
        ans += tmp
    return ans / factorial(N)


print((c_average_length()))

def c_average_length():
    N = int(eval(input()))
    Positions = [[int(i) for i in input().split()] for j in range(N)]
    ans = 0.0
    for i in range(N):
        for j in range(i + 1, N):
            ans += (
                (Positions[i][0] - Positions[j][0]) ** 2
                + (Positions[i][1] - Positions[j][1]) ** 2
            ) ** 0.5
    return ans * 2 / N


print((c_average_length()))

-    from itertools import permutations -    from math import factorial - -    for route in permutations(list(range(N)), N): -        tmp = 0.0 -        for i in range(N - 1): -            cur_v = route[i] -            next_v = route[i + 1] -            tmp += ( -                (Positions[next_v][0] - Positions[cur_v][0]) ** 2 -                + (Positions[next_v][1] - Positions[cur_v][1]) ** 2 +    for i in range(N): +        for j in range(i + 1, N): +            ans += ( +                (Positions[i][0] - Positions[j][0]) ** 2 +                + (Positions[i][1] - Positions[j][1]) ** 2 -        ans += tmp -    return ans / factorial(N) +    return ans * 2 / N