#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const int mod = 1e9 + 7;




int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int n;
    cin >> n;
    vector<pair<int, int>> a(52, {100, -100});
    vector<pair<int, int>> dp(52, {1e9, 1e9});
    vector<bool> flag(51);
    for(int i = 0; i < n; ++i){
        int x, y;
        cin >> x >> y;
        flag[y] = true;
        a[y].first = min(x, a[y].first);
        a[y].second = max(x, a[y].second);
    }
    int st = -1;
    for(int i = 1; i <= 50; ++i){
        if(flag[i]){
            dp[i].first = abs(i - 1) + abs(a[i].second - 1) + abs(a[i].second - a[i].first);
            dp[i].second = abs(i - 1) + abs(a[i].first - 1) + abs(a[i].second - a[i].first);
            st = i + 1;
            break;
        }
    }
    int pr = st - 1;
    for(int i = st; i <= 50; ++i){
        if(flag[i]){
            dp[i].first = min(dp[pr].first + abs(i - pr) + abs(a[i].second - a[pr].first) + abs(a[i].second - a[i].first), dp[i].first);
            dp[i].first = min(dp[i].first, dp[pr].second + abs(i - pr) + abs(a[i].second - a[pr].second) + abs(a[i].second - a[i].first));
            dp[i].second = min(dp[pr].first + abs(i - pr) + abs(a[i].first - a[pr].first) + abs(a[i].second - a[i].first), dp[i].second);
            dp[i].second = min(dp[i].second, dp[pr].second + abs(i - pr) + abs(a[i].first - a[pr].second) + abs(a[i].second - a[i].first));
            pr = i;
        }

    }
    cout << min(dp[pr].first, dp[pr].second) << "\n";
}