import java.util.*;

public class Main{
  public static void main(String[] args) {

    Scanner sc = new Scanner(System.in);
    int n, m;
    n = sc.nextInt();
    m = sc.nextInt();

    int x, y, l, r;
    l = 0;
    r = (int)1E5 + 10;

    for (int i = 0; i < m; i++) {
      x = sc.nextInt();
      y = sc.nextInt();
      l = Math.max(x, l);
      r = Math.min(y, r);
    }

    System.out.println(l <= r ? r - l + 1 : 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