import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();
		int ans;
		int[] key = new int[n];
		for(int i = 1; i <=n; i++) {
			key[i-1] = i;
		}
		int maxL = 0;
		int minR = n;
		for(int i = 0; i < m; i++) {
			maxL = Math.max(maxL, sc.nextInt());
			minR = Math.min(minR, sc.nextInt());
		}
		ans = minR-maxL+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