#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;}