course bouclée

import java.util.*;
import java.io.*;
import java.math.*;
class Solution {

    public static void main(String args[]) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int xTab[] = new int[n];
        int yTab[] = new int[n];
        for (int i = 0; i < n; i++) {
            xTab[i] = in.nextInt();
            yTab[i] = in.nextInt();

        }
        double distance = 0;
        //double last = 0.0;
        int xLast =0;
        int yLast = 0;
        for(int i = 0; i < n-1; i++)
        {
             distance += Math.sqrt((xTab[i]-xTab[i+1])*(xTab[i]-xTab[i+1]) + (yTab[i]-yTab[i+1])*(yTab[i]-yTab[i+1]));
             if(i == n-2)
             {
                 xLast = xTab[i+1];
                 yLast = yTab[i+1];
             }

        }
        distance += Math.sqrt( (xTab[0]-xLast)*(xTab[0]-xLast) + (yTab[0]-yLast)*(yTab[0]-yLast)  );
        int distanceI = (int) distance;
        if(distanceI - distance == 0)
            System.out.println(distanceI);
        else
        System.out.printf("%.3f",distance);
    }
}