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(rights[i]), Math.max(graph.getOrDefault(compress.get(rights[i]), 0), compress.get(lefts[i])));
        }
        int[] costs = new int[size];
        for (int i = 1; i < size; i++) {
            if (graph.containsKey(i)) {
                costs[i] = Math.max(costs[i - 1], costs[graph.get(i)] + 1);
            } else {
                costs[i] = costs[i - 1];
            }
        }
        System.out.println((n - 1) * 2 - costs[size - 1]);
    }
}
    
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();
    }
    
}