#pragma comment(linker, "/STACK:1024000000,1024000000")

#include <cstdio>

#include <string>

#include <cstdlib>

#include <cmath>

#include <iostream>

#include <cstring>

#include <set>

#include <queue>

#include <algorithm>

#include <vector>

#include <map>

#include <cctype>

#include <stack>

using namespace std ;

typedef long long LL;

typedef pair<int, int> P;

const int INF = 0x3f3f3f3f;

const double inf = 0x3f3f3f3f3f3f;

const double PI = acos(-1.0);

const double eps = 1e-10;

const int maxn = 4e5 + 5;

const int mod = 1e9 + 7;

const double sqrt2 = sqrt(2.0);

const char *mark = "+-*";

const int dr[] = {-1, 0, 1, 0};

const int dc[] = {0, 1, 0, -1};

int n, m;

inline bool is_in(int r, int c){

    return r >= 0 && r < n && c >= 0 && c < m;

}

inline double add(double a, double b){

    if(abs(a+b) < eps * (abs(a) + abs(b)))  return 0;

    return a + b;

}

struct Point{

    double x, y;

    Point(){ }

    Point(double xx, double yy) : x(xx), y(yy) { }

    Point operator + (Point p){

        return Point(add(x, p.x), add(y, p.y));

    }

    Point operator - (Point p){

        return Point(add(x, -p.x), add(y, -p.y));

    }

    double dot(Point p){

        return add(x*p.x, -y*p.y);

    }

    double det(Point p){

        return add(x*p.y, -y*p.x);

    }

};

bool cmp(const Point &lhs, const Point &rhs){

    if(lhs.x != rhs.x)  return lhs.x < rhs.x;

    return lhs.y < rhs.y;

}

vector<Point> convex_hull(Point *ps, int n){

    sort(ps, ps+n, cmp);

    int k = 0;

    vector<Point> qs(n*2);

    for(int i = 0; i < n; ++i){

        while(k > 1 && (qs[k-1] - qs[k-2]).det(ps[i] - qs[k-1]) <= 0)  --k;

        qs[k++] = ps[i];

    }

    for(int i = n-2, t = k; i >= 0; --i){

        while(k > t && (qs[k-1]-qs[k-2]).det(ps[i]-qs[k-1]) <= 0)  --k;

        qs[k++] = ps[i];

    }

    qs.resize(k-1);

    return qs;

}

double dist(Point p, Point q){

    return (p-q).dot(p-q);

}

Point ps[maxn];

double solve(int n){

    vector<Point> qs = convex_hull(ps, n);

    double ans = 0;

    int m = qs.size();

    for(int i = 0; i < m; ++i){

        int x = abs(qs[i].x - qs[(i+1)%m].x);

        int y = abs(qs[i].y - qs[(i+1)%m].y);

        ans += abs(x-y);

        ans += 1.0*min(x, y) * sqrt2;

    }

    return ans;

}

int main(){

    while(scanf("%d", &n) == 1){

        int cnt = 0;

        for(int i = 0; i < n; ++i){

            double x, y;

            scanf("%lf %lf", &x, &y);

            ps[cnt++] = Point(x+1, y);

            ps[cnt++] = Point(x, y+1);

            ps[cnt++] = Point(x, y-1);

            ps[cnt++] = Point(x-1, y);

        }

        printf("%.6f\n", solve(cnt));

    }

    return 0;

}