import java.util.*;
public class Main{
    public static void main(String[] args){
        Scanner scan = new Scanner(System.in);
        int l = scan.nextInt() + 1;
        int m = scan.nextInt();
        int arr[] = new int[2 * m];
        for (int i = 0; i < arr.length; i++){
            arr[i] = scan.nextInt();
        }
        for (int i = 2; i < arr.length; i = i + 2) {
            if (arr[i] < arr[0] && arr[i + 1] > arr[0] && arr[i + 1] < arr[1]){
                arr[0] = arr[i];
            }else if (arr[i] >arr[0] && arr[i] < arr[1] && arr[i + 1] > arr[1]) {
                arr[1] = arr[i + 1];
            }else{
                continue;
            }
            arr[i] = arr[i + 1] = 0;
        }
        int sum = 0;
        for (int i = 1; i < arr.length; i = i + 2){
            if (arr[i] == 0) {
                continue;
            }
            sum += arr[i] - arr[i - 1] + 1;
        }
        System.out.println(l - sum);
    }
}