import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scn = new Scanner(System.in);
		int n = scn.nextInt();
		int m = scn.nextInt();
		int max = n;
		int min = 0;
		int l;
		int r;
		for(;0<m;m--) {
			l = scn.nextInt();
			r = scn.nextInt();
			if(min<l) {
				min = l;
			}
			if(r<max) {
				max = r;
			}
		}
		if(max-min<0) {
			System.out.println(0);
		}else {
			System.out.println(max-min + 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