import java.util.Comparator;
import java.util.PriorityQueue;
import java.util.Scanner;

public class Main {

    public static void main(String args[]) {

        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int m = Integer.parseInt(sc.next());
        PriorityQueue<Integer> l = new PriorityQueue<>(Comparator.reverseOrder());
        PriorityQueue<Integer> r = new PriorityQueue<>();
        for (int i = 0; i < m; i++) {
            l.add(Integer.parseInt(sc.next()));
            r.add(Integer.parseInt(sc.next()));
        }

        int result = r.peek() - l.peek() + 1;

        System.out.println(result < 0 ? 0 : result);
    }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz