#include <cstdio>

#include <cstring>

#include <cmath>

#include <string>

#include <iostream>

#include <algorithm>

#include <string>

using namespace std;

#define rep(i, n) for(int i=0; i<(n); ++i)

#define for1(i,a,n) for(int i=(a);i<=(n);++i)

#define for2(i,a,n) for(int i=(a);i<(n);++i)

#define for3(i,a,n) for(int i=(a);i>=(n);--i)

#define for4(i,a,n) for(int i=(a);i>(n);--i)

#define CC(i,a) memset(i,a,sizeof(i))

#define read(a) a=getint()

#define print(a) printf("%d", a)

#define dbg(x) cout << #x << " = " << x << endl

#define printarr(a, n, m) rep(aaa, n) { rep(bbb, m) cout << a[aaa][bbb]; cout << endl; }

inline const int getint() { int r=0, k=1; char c=getchar(); for(; c<'0'||c>'9'; c=getchar()) if(c=='-') k=-1; for(; c>='0'&&c<='9'; c=getchar()) r=r*10+c-'0'; return k*r; }

inline const int max(const int &a, const int &b) { return a>b?a:b; }

inline const int min(const int &a, const int &b) { return a<b?a:b; }

using namespace std;

void setio(string name){

	string in = name + ".in", out = name + ".out";

	ios::sync_with_stdio(false);

	freopen(in.c_str(), "r", stdin);

	freopen(out.c_str(), "w", stdout);

}

const int N=10005;

struct node {

	double x, y;

	node(const double &_x=0, const double &_y=0) : x(_x), y(_y) {}

}st[N], p[N];

int cnt, n;

node operator - (const node &a, const node &b) { return node(a.x-b.x, a.y-b.y); }

double cross(const node &a, const node &b) { return a.x*b.y-b.x*a.y; }

const bool cmp(const node &a, const node &b) { return (a.x==b.x)?(a.y<b.y):(a.x<b.x); }

const double dis(const node &a, const node &b) { return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y)); }

void tubao() {

	sort(p, p+n, cmp);

	cnt=0;

	rep(i, n) {

		while(cnt>1 && cross(st[cnt-1]-st[cnt-2], p[i]-st[cnt-2])<=0) --cnt;

		st[cnt++]=p[i];

	}

	int k=cnt;

	for3(i, n-2, 0) {

		while(cnt>k && cross(st[cnt-1]-st[cnt-2], p[i]-st[cnt-2])<=0) --cnt;

		st[cnt++]=p[i];

	}

	if(n>1) --cnt;

}

int main() {

	setio("fc");

	scanf("%d", &n);

	rep(i, n) scanf("%lf%lf", &p[i].x, &p[i].y);

	tubao();

	double ans=0;

	for1(i, 0, cnt-1) ans+=dis(st[i], st[i+1]);

	printf("%.2lf\n", ans);

	return 0;

}