import java.util.*;

class Main {
  public static void main(String args[]) {
    Scanner sc = new Scanner(System.in);

    int N = sc.nextInt();
    int M = sc.nextInt();
    int G[] = new int[N+2];
    for (int i = 0; i < M; i++) {
      G[sc.nextInt()]++;
      G[sc.nextInt()+1]--;
    }
    int count = 0;
    for (int i = 1; i < N+2; i++) {
      if (i > 0) {
        G[i] += G[i - 1];
      }
      if (G[i] == M) count++;
    }
    System.out.println(count);
  }
}

/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