import java.util.*;
class joi2019_ho_t4 {
public static int minStepsRecur(int[] coinsX, int[] coinsY, int[] targetX, int[] targetY, int l, int r) {
if (l >= r) return 0;
int m = l;
for (int i = l; i < r; i++) {
if (coinsX[i] < coinsX[m]) {
m = i;
}
}
return Math.min(r - l,
minStepsRecur(coinsX, coinsY, targetX, targetY, l, m) +
minStepsRecur(coinsX, coinsY, targetX, targetY, m + 1, r) +
Math.abs(coinsX[m] - targetX[m]) + Math.abs(coinsY[m] - targetY[m]));
}
public static int minSteps(int[] coinsX, int[] coinsY, int N) {
int[] targetX = new int[N];
int[] targetY = new int[2 * N];
// Generamos las posiciones de destino de las monedas
for (int i = 0; i < N; i++) {
targetX[i] = i + 1; // Las posiciones en X son 1..N
targetY[i] = 1; // La primera columna de destino
targetY[N + i] = 2; // La segunda columna de destino
}
return minStepsRecur(coinsX, coinsY, targetX, targetY, 0, N);
}
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int N = sc.nextInt();
int[] coinsX = new int[2 * N];
int[] coinsY = new int[2 * N];
for (int i = 0; i < 2 * N; i++) {
coinsX[i] = sc.nextInt();
coinsY[i] = sc.nextInt();
}
System.out.println(minSteps(coinsX, coinsY, N));
sc.close();
}
}
