import java.io.*;
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        int m = sc.nextInt();
        int[] lefts = new int[m];
        int[] rights = new int[m];
        TreeMap<Integer, Integer> compress = new TreeMap<>();
        for (int i = 0; i < m; i++) {
            lefts[i] = sc.nextInt();
            rights[i] = sc.nextInt();
            compress.put(lefts[i], null);
            compress.put(rights[i], null);
        }
        int size = 0;
        for (int x : compress.keySet()) {
            compress.put(x, size++);
        }
        HashMap<Integer, Integer> graph = new HashMap<>();
        for (int i = 0; i < m; i++) {
            graph.put(compress.get(lefts[i]), Math.min(graph.getOrDefault(compress.get(lefts[i]), Integer.MAX_VALUE), compress.get(rights[i])));
        }
        int[] costs = new int[size];
        PriorityQueue<Path> queue = new PriorityQueue<>();
        queue.add(new Path(0, 1));
        while (queue.size() > 0) {
            Path p = queue.poll();
            if (costs[p.idx] >= p.value) {
                continue;
            }
            costs[p.idx] = p.value;
            if (graph.containsKey(p.idx)) {
                queue.add(new Path(graph.get(p.idx), p.value + 1));
            }
            if (p.idx < size - 1) {
                queue.add(new Path(p.idx + 1, p.value));
            }
        }
        System.out.println((n - 1) * 2 - costs[size - 1] + 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) {
            if (value == another.value) {
                return idx - another.idx;
            } else {
                return another.value - value;
            }
        }
    }
}
    
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    StringBuilder sb = new StringBuilder();
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public String next() throws Exception {
        while (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
    
}