#define _CRT_SECURE_NO_WARNINGS 1
#include<iostream>
#include<string>
#include<cstdlib>
#include<cstdio>
#include<cmath>
using namespace std;
class Point {
public:
float x,y;
};
class Polygon
{
private:
int nLength;
Point *Vertex;
public:
Polygon(int n)
{
nLength=n;
}
void Set(int idx,Point pnt)
{
Vertex=(Point*)malloc(sizeof(Point)*nLength);
int t=idx;
Vertex[t]=pnt;
}
float Perimeter()
{
float cau=0;
int h=0;
for(h=0;h<nLength;h++)
{
cau=cau+sqrt(pow((Vertex[h].x-Vertex[h+1].x),2)+pow((Vertex[h].y-Vertex[h+1].y),2));
}
cau=cau+sqrt(pow((Vertex[0].x-Vertex[nLength-1].x),2)+pow((Vertex[0].y-Vertex[nLength-1].y),2));
return cau;
}
};
int main()
{
int n =0;
Point pnt;
cin >> n;
Polygon po(n);
for(int i=0;i<n;i++)
{
cin >> pnt.x >>pnt.y;
po.Set(i, pnt);
}
printf("%4.1f", po.Perimeter());
return 1;
}