import java.util.Scanner;

public class Main {
	long c[];
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int M = sc.nextInt();
		int min, max ;
		min =1;
		max =N;
		for (int i =0;i<M;i++) {
			int x,y;
			x= sc.nextInt();
			y =sc.nextInt();
			if (x>min) {
				min =x;
			}
			if (y<max) {
				max =y;
			}
		}
		if (max<min) {
			System.out.println(0);
			return ;
		}
		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