import java.util.Arrays;
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());
		int[] l = new int[m];
		int[] r = new int[m];
		for (int i = 0; i < m; i++) {
			l[i] = Integer.parseInt(sc.next());
			r[i] = Integer.parseInt(sc.next());
		}

		int ans = Arrays.stream(r).min().getAsInt() - Arrays.stream(l).max().getAsInt() + 1;

		System.out.println(Math.max(ans, 0));

	}

}

/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