import java.util.*;
class Main{
	public static void main(String[] args){
		Scanner sc=new Scanner(System.in);
		int n=sc.nextInt();
		int m=sc.nextInt();
		int[] l=new int[m];
		int[] r=new int[m];
		for(int i=0;i<m;i++){
			l[i]=sc.nextInt();
			r[i]=sc.nextInt();
		}
		int maxl=0;
		int minr=n;
		for(int i=0;i<m;i++){
			if(maxl<l[i])
				maxl=l[i];
		}
		for(int i=0;i<m;i++){
			if(minr>r[i])
				minr=r[i];
		}
		int count=0;
		for(int i=1;i<=n;i++){
			if(maxl<=i&&i<=minr)
				count++;
		}
		System.out.println(count);
	}
}
/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