import java.util.Scanner;

public class Main{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int m = Integer.parseInt(sc.next());
        int min = n+1;
        int max = 0;
        int l,r;
        for(int i=0;i<m;i++){
            l = Integer.parseInt(sc.next());
            r = Integer.parseInt(sc.next());
            min = Math.min(r,min);
            max = Math.max(l,max);
        }
        if(min-max>=0){
            System.out.println(min-max+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