n = gets.to_i
xy = n.times.map{gets.split.map(&:to_i)}

sum = 0
xy.permutation(n){|z|
  cost = 0
  (n-1).times.map{|i|
    xd = (z[i][0] - z[i+1][0])**2
    yd = (z[i][1] - z[i+1][1])**2
    cost += Math.sqrt(xd+yd)
  }
  sum += cost
}

p sum/((1..n).map.inject(:*))
