import java.util.Arrays;
import java.util.Scanner;

public class Main {

    public static void main(String args[]) {

        // 入力
        Scanner sc = new Scanner(System.in);
        Integer n = Integer.parseInt(sc.next());
        Integer m = Integer.parseInt(sc.next());
        Integer[] l = new Integer[m];
        Integer[] r = new Integer[m];
        for (int i = 0; i < m; i++) {
            l[i] = Integer.parseInt(sc.next());
            r[i] = Integer.parseInt(sc.next());
        }

        // 主処理
        Arrays.sort(l);
        Arrays.sort(r);

        int min = l[m - 1];
        int max = r[0];

        int result = max - min + 1 < 0 ? 0 : Math.min(max - min + 1, n);

        // 出力
        System.out.println(result);
        sc.close();
    }
}
/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