import java.util.*;
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];
    int r[] = new int[m];
    for(int i=0;i<m;i++){
      l[i]=sc.nextInt();
      r[i]=sc.nextInt();
    }
    Arrays.sort(l);
    Arrays.sort(r);
    int answer = r[0]-l[m-1]+1;
    if(answer<0){
      answer=0;
    }
    System.out.println(answer);
  }
} import java.util.*; util.* java 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];
    int r[] = new int[m];
    for(int i=0;i<m;i++){
      l[i]=sc.nextInt();
      r[i]=sc.nextInt();
    }
    Arrays.sort(l);
    Arrays.sort(r);
    int answer = r[0]-l[m-1]+1;
    if(answer<0){
      answer=0;
    }
    System.out.println(answer);
  }
} 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];
    int r[] = new int[m];
    for(int i=0;i<m;i++){
      l[i]=sc.nextInt();
      r[i]=sc.nextInt();
    }
    Arrays.sort(l);
    Arrays.sort(r);
    int answer = r[0]-l[m-1]+1;
    if(answer<0){
      answer=0;
    }
    System.out.println(answer);
  } main {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int m = sc.nextInt();
    int l[] = new int[m];
    int r[] = new int[m];
    for(int i=0;i<m;i++){
      l[i]=sc.nextInt();
      r[i]=sc.nextInt();
    }
    Arrays.sort(l);
    Arrays.sort(r);
    int answer = r[0]-l[m-1]+1;
    if(answer<0){
      answer=0;
    }
    System.out.println(answer);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int m = sc.nextInt(); m sc.nextInt() sc.nextInt sc int l[] = new int[m]; l new int[m] m int r[] = new int[m]; r new int[m] m for(int i=0;i<m;i++){
      l[i]=sc.nextInt();
      r[i]=sc.nextInt();
    } int i=0; int i=0; i 0 i<m i m i++ i++ i {
      l[i]=sc.nextInt();
      r[i]=sc.nextInt();
    } {
      l[i]=sc.nextInt();
      r[i]=sc.nextInt();
    } l[i]=sc.nextInt() l[i] l i sc.nextInt() sc.nextInt sc r[i]=sc.nextInt() r[i] r i sc.nextInt() sc.nextInt sc Arrays.sort(l) Arrays.sort Arrays l Arrays.sort(r) Arrays.sort Arrays r int answer = r[0]-l[m-1]+1; answer r[0]-l[m-1]+1 r[0]-l[m-1] r[0] r 0 l[m-1] l m-1 m 1 1 if(answer<0){
      answer=0;
    } answer<0 answer 0 {
      answer=0;
    } answer=0 answer 0 System.out.println(answer) System.out.println System.out System System.out answer String[] args args 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];
    int r[] = new int[m];
    for(int i=0;i<m;i++){
      l[i]=sc.nextInt();
      r[i]=sc.nextInt();
    }
    Arrays.sort(l);
    Arrays.sort(r);
    int answer = r[0]-l[m-1]+1;
    if(answer<0){
      answer=0;
    }
    System.out.println(answer);
  }
} 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];
    int r[] = new int[m];
    for(int i=0;i<m;i++){
      l[i]=sc.nextInt();
      r[i]=sc.nextInt();
    }
    Arrays.sort(l);
    Arrays.sort(r);
    int answer = r[0]-l[m-1]+1;
    if(answer<0){
      answer=0;
    }
    System.out.println(answer);
  }
} Main
import java.util.*;
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];
    int r[] = new int[m];
    for(int i=0;i<m;i++){
      l[i]=sc.nextInt();
      r[i]=sc.nextInt();
    }
    Arrays.sort(l);
    Arrays.sort(r);
    int answer = r[0]-l[m-1]+1;
    if(answer<0){
      answer=0;
    }
    System.out.println(answer);
  }
}