require 'bigdecimal/math'

N = gets.to_i
z = [nil]

N.times do
  z << gets.split.map(&:to_i)
end

def dist(z1, z2)
  BigMath::sqrt(BigDecimal((z1[0] - z2[0])**2 + (z1[1] - z2[1])**2), 6)
end

sum = 0

[*1..N].permutation(N) do |i|
  i.inject { |j, k| sum += dist(z[j], z[k]); k }
end

puts (sum / [*1..N].inject(:*)).to_s 'F'