package main

import (
	"fmt"
	"math"
)

func circle(x1, y1, x2, y2 float64) float64 {
	return math.Hypot(x2-x1, y2-y1)
}

func main() {
	var n int
	fmt.Scan(&n)

	if n <= 0 {
		fmt.Println("0.00")
		return
	}
	if n == 1 {
		fmt.Println("0.00")
		return
	}

	var x1, y1 float64
	fmt.Scan(&x1, &y1)

	if n == 2 {
		var x2, y2 float64
		fmt.Scan(&x2, &y2)
		fmt.Printf("%.2f\n", circle(x1, y1, x2, y2))
		return
	}

	firstX, firstY := x1, y1
	total := 0.0
	for i := 1; i < n; i++ {
		var x2, y2 float64
		fmt.Scan(&x2, &y2)
		total += circle(x1, y1, x2, y2)
		x1, y1 = x2, y2
	}
	total += circle(x1, y1, firstX, firstY)

	fmt.Printf("%.2f\n", total)
}