import java.util.Scanner;

/**
 * Main
 */
public 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+1];
        int[] R = new int[M+1];
        int[] countID = new int[N+1];
        int under = 0;
        int upper = N;

        for(int i=1; i<=M; i++){
            L[i] = sc.nextInt();
            R[i] = sc.nextInt();
            under = Math.max(under,L[i]);
            upper = Math.min(upper,R[i]);
        }
        sc.close();

        // for(int i=1; i<=M; i++){
        //     for(int j=L[i]; j <= R[i]; j++){
        //         countID[j]++;
        //     }
        // }

        int ans = upper - under + 1;
        if(ans <= 0){
            System.out.println("0");
        }else{
            System.out.println(ans);
        }
        // for(int i=1; i<=N; i++){
        //     if(countID[i] == M){
        //         ans++;
        //     }
        // }
    }
}
/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