import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int m = sc.nextInt();

        int min = 0;
        int max = 1_000_000;
        for (int i = 0; i < m; i++) {
            int l = sc.nextInt();
            int r = sc.nextInt();
            if (l > min) {
                min = l;
            }
            if (r < max) {
                max = r;
            }
        }
        sc.close();

        int ans;
        if (max < min) {
            ans = 0;
        } else {
            ans = max - min + 1;
        }
        System.out.println(ans);
    }

}

/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