import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner scn = new Scanner(System.in);
    int N = scn.nextInt();
    int M = scn.nextInt();

    int Lmax = scn.nextInt();
    int Rmin = scn.nextInt();
    for (int i = 1; i < M; i++) {
      int L = scn.nextInt();
      if (L > Lmax) {
        Lmax = L;
      }
      int R = scn.nextInt();
      if (R < Rmin) {
        Rmin = R;
      }
    }

    if (Rmin - Lmax < 0) {
      System.out.println(0);
    } else {
      System.out.println(Rmin - Lmax + 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