

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		int m = sc.nextInt();

		int left = 1;
		int right = n;
		for(int i = 0; i < m; i++){
			int l = sc.nextInt();
			int r = sc.nextInt();

			if(l > right || r < left){
				System.out.println(0);
				return;
			}

			left = Math.max(l, left);
			right = Math.min(r, right);
		}

		System.out.println(right - left + 1);
	}

}

/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