import java.util.Scanner;

public class Main {

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

		int card = sc.nextInt();
		int gate = sc.nextInt();
		int min = 100000;
		int max = 0;

		int[] L = new int[gate];
		int[] R = new int[gate];
		for(int i = 0; i<gate; i++) {
			L[i] = sc.nextInt();
			R[i] = sc.nextInt();
		}
		for(int i=0; i<gate; i++) {
				max = Math.max(L[i], max);
				min = Math.min(R[i], min);
		}
			int anser = Math.max((min-max)+1, 0);
			System.out.println(anser);
		}

	}
/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