import java.io.*;
import java.util.*;
import java.util.function.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int h = sc.nextInt();
        int w = sc.nextInt();
        int n = sc.nextInt();
        Point start = new Point(0, 0);
        Point[] points = new Point[n * 2 + 2];
        for (int i = 0; i < n * 2; i++) {
            points[i] = new Point(sc.nextInt(), sc.nextInt());
        }
        points[n * 2] = new Point(1, 1);
        points[n * 2 + 1] = new Point(h, w);
        PriorityQueue<Path> queue = new PriorityQueue<>();
        queue.add(new Path(n * 2, 0));
        int[] costs = new int[n * 2 + 2];
        Arrays.fill(costs, Integer.MAX_VALUE);
        while (queue.size() > 0) {
            Path p = queue.poll();
            if (costs[p.idx] <= p.value) {
                continue;
            }
            costs[p.idx] = p.value;
            for (int i = 0; i < n * 2 + 2; i++) {
                if (costs[i] == Integer.MAX_VALUE) {
                    queue.add(new Path(i, p.value + points[p.idx].getDistance(points[i])));
                }
            }
            if (p.idx < n * 2 && p.idx % 2 == 0) {
                queue.add(new Path(p.idx + 1, p.value + 1));
            }
        }
        System.out.println(costs[n * 2 + 1]);
    }
    
    static class Path implements Comparable<Path> {
        int idx;
        int value;
        
        public Path(int idx, int value) {
            this.idx = idx;
            this.value = value;
        }
        
        public int compareTo(Path another) {
            return value - another.value;
        }
    }
    
    static class Point {
        int x;
        int y;
        
        public Point(int x, int y) {
            this.x = x;
            this.y = y;
        }
        
        public int getDistance(Point p) {
            return Math.abs(x - p.x) + Math.abs(y - p.y);
        }
    }
}
class Scanner {
    BufferedReader br;
    StringTokenizer st = new StringTokenizer("");
    StringBuilder sb = new StringBuilder();
    
    public Scanner() {
        try {
            br = new BufferedReader(new InputStreamReader(System.in));
        } catch (Exception e) {
            
        }
    }
    
    public int nextInt() {
        return Integer.parseInt(next());
    }
    
    public long nextLong() {
        return Long.parseLong(next());
    }
    
    public double nextDouble() {
        return Double.parseDouble(next());
    }
    
    public String next() {
        try {
            while (!st.hasMoreTokens()) {
                st = new StringTokenizer(br.readLine());
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            return st.nextToken();
        }
    }
    
}