n = gets.to_i
x = Array.new(n).map{ Array.new(2) }
n.times do |i|
    x[i][0], x[i][1] = gets.split.map(&:to_i)
end

d = Array.new(n).map{ Array.new(n) }
n.times do |i|
    n.times do |j|
        d[i][j] = Math.sqrt((x[i][0] - x[j][0]) ** 2 + (x[i][1] - x[j][1]) ** 2)
    end
end

puts d.map{ |e| e.inject(:+)}.inject(:+)/n