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 min = 2147483647;
        int max = 0;
        for (int index=0; index<M; index++){
            
            int left = sc.nextInt();
            int right = sc.nextInt();
            if (left>max){
                max=left;
            }
            if (right<min){
                min=right;
            }
        }
        
        if (min<max){
            System.out.println("0");
        } else {
            System.out.println(min-max+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