import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int m = sc.nextInt();
      
        int a = sc.nextInt();      
        int b = sc.nextInt();
        
        while(sc.hasNextInt()){
            int hidari = sc.nextInt();
            int migi = sc.nextInt();
            if(a < hidari){
              a = hidari;
            }
            if(migi < b ){
              b = migi; 
            }
        }
        if(b-a+1>0){
            System.out.println(b - a + 1);
        }else{
            System.out.println(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