import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int min = 1;
		int max = in.nextInt();
		int gate = in.nextInt();
		int cch;
		for (int i = 0; i < gate; i++) {
			for (int j = 0; j < 2; j++) {
				cch = in.nextInt();
				if (j == 0) {
					if (min < cch) min = cch;
				} else {
					if (max > cch) max = cch;
				}
			}
		}
		in.close();
		int ans = max - min + 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