#include<bits/stdc++.h>

#define LL long long

#define fi first

#define se second

#define mk make_pair

#define PLL pair<LL, LL>

#define PLI pair<LL, int>

#define PII pair<int, int>

#define SZ(x) ((int)x.size())

#define ull unsigned long long

using namespace std;

const int N =  + ;

const int inf = 0x3f3f3f3f;

const LL INF = 0x3f3f3f3f3f3f3f3f;

const int mod = 1e9 + ;

const double eps = 1e-;

const double PI = acos(-);

int dp[][][][][][];

int n, a[N], b[N];

int cur = , lst = ;

inline bool chkmin(int &a, int b) {

    return a > b ? a = b, true : false;

}

int main() {

    scanf("%d", &n);

    for(int i = ; i <= n; i++) scanf("%d%d", &a[i], &b[i]);

    memset(dp[cur], inf, sizeof(dp[cur]));

    dp[cur][][][][][] =  * n;

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

        swap(cur, lst);

        memset(dp[cur], inf, sizeof(dp[cur]));

        for(int c1 = ; c1 >= ; c1--) {

            for(int c2 = ; c2 >= ; c2--) {

                for(int c3 = ; c3 >= ; c3--) {

                    for(int c4 = ; c4 >= ; c4--) {

                        for(int f = ; f <= ; f++) {

                            int& ret = dp[lst][f][c1][c2][c3][c4];

                            if(ret >= inf) continue;

                            if(!c1 && i < n) {

                                chkmin(dp[cur][a[i + ]][b[i + ]][c2][c3][c4], ret + abs(f - a[i + ]));

                            } else if(c1) {

                                chkmin(dp[lst][c1][][c2][c3][c4], ret + abs(f - c1));

                            }

                            if(!c2 && i < n) {

                                chkmin(dp[cur][a[i + ]][c1][b[i + ]][c3][c4], ret + abs(f - a[i + ]));

                            } else if(c2) {

                                chkmin(dp[lst][c2][c1][][c3][c4], ret + abs(f - c2));

                            }

                            if(!c3 && i < n) {

                                chkmin(dp[cur][a[i + ]][c1][c2][b[i + ]][c4], ret + abs(f - a[i + ]));

                            } else if(c3) {

                                chkmin(dp[lst][c3][c1][c2][][c4], ret + abs(f - c3));

                            }

                            if(!c4 && i < n) {

                                chkmin(dp[cur][a[i + ]][c1][c2][c3][b[i + ]], ret + abs(f - a[i + ]));

                            } else if(c4) {

                                chkmin(dp[lst][c4][c1][c2][c3][], ret + abs(f - c4));

                            }

                        }

                    }

                }

            }

        }

    }

    int ans = inf;

    for(int i = ; i <= ; i++)

        ans = min(ans, dp[lst][i][][][][]);

    printf("%d\n", ans);

    return ;

}

/*

*/