#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>

// @author: Danielto1404

#define c_boost std::ios_base::sync_with_stdio(false); std::cin.tie(nullptr)

using namespace std;

struct point {
    int x, y;
};

double size(point a, point b) {
    int hyp_cnt = min(abs(a.x - b.x), abs(a.y - b.y));
    int max_size = max(abs(a.x - b.x), abs(a.y - b.y));
    return sqrt(2) * hyp_cnt + (max_size - hyp_cnt);
}

bool negative(point a, point b, point c) {
    return a.x * (b.y - c.y) + b.x * (c.y - a.y) + c.x * (a.y - b.y) < 0;
}

bool positive(point a, point b, point c) {
    return a.x * (b.y - c.y) + b.x * (c.y - a.y) + c.x * (a.y - b.y) > 0;
}

void find_min_shell(vector<point> &points) {
    if (points.size() == 1) return;

    sort(points.begin(), points.end(), [](point a, point b) {
        return a.x < b.x || (a.x == b.x && a.y < b.y);
    });

    point left = points.front(), right = points.back();
    vector<point> up, down;
    up.push_back(left);
    down.push_back(left);

    for (int i = 1; i < points.size(); ++i) {
        if (i == points.size() - 1 || negative(left, points[i], right)) {
            while (up.size() >= 2 && !negative(up[up.size() - 2], up.back(), points[i]))
                up.pop_back();

            up.push_back(points[i]);
        }
        if (i == points.size() - 1 || positive(left, points[i], right)) {
            while (down.size() >= 2 && !positive(down[down.size() - 2], down.back(), points[i]))
                down.pop_back();

            down.push_back(points[i]);
        }
    }

    points.clear();
    for (const point p : up)
        points.push_back(p);

    for (int i = (int) down.size() - 2; i > 0; --i)
        points.push_back(down[i]);
}

int main() {
    c_boost;
    int n, x, y;
    cin >> n;
    vector<point> points;
    for (int i = 0; i < n; ++i) {
        cin >> x >> y;
        points.push_back({x + 1, y});
        points.push_back({x - 1, y});
        points.push_back({x, y + 1});
        points.push_back({x, y - 1});
    }

    find_min_shell(points);

    double perimeter = 0;
    for (int i = 0; i < points.size() - 1; ++i) {
        perimeter += size(points[i], points[i + 1]);
    }
    perimeter += size(points.back(), points.front());
    cout << perimeter;
}