import java.util.Scanner;

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

            int ll = 0;
            int rr = n;
            for (int i = 0; i < m; i++) {
                int li = sc.nextInt();
                int ri = sc.nextInt();
                if (li > ll) {
                    ll = li;
                }
                if (ri < rr) {
                    rr = ri;
                }
            }
            int ans = rr - ll + 1;
            if (ans < 0) {
                ans = 0;
            }
            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