object Solution {
    def main(args: Array[String]) {
      def len(x: Array[Double], y: Array[Double]): Double = {
        math.sqrt(math.pow(x(0) - y(0), 2) + math.pow(x(1) - y(1), 2))
      }
      val n = io.StdIn.readLine.toInt
      val arr = (1 to n).map(_ => io.StdIn.readLine.split(" ").map(_.toDouble))
      val p = (0 until n).map(x => len(arr(x), arr((x + 1) % n))).sum
      println(p)
    }
}