import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int A = sc.nextInt();
    int B = sc.nextInt();
    int C = sc.nextInt();
    int D = sc.nextInt();
    
    int ans = Math.min(B, D) - Math.max(A, C);
    System.out.println(ans > 0 ? ans : 0);
  }
} import java.util.*; util.* java public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int A = sc.nextInt();
    int B = sc.nextInt();
    int C = sc.nextInt();
    int D = sc.nextInt();
    
    int ans = Math.min(B, D) - Math.max(A, C);
    System.out.println(ans > 0 ? ans : 0);
  }
} Main public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int A = sc.nextInt();
    int B = sc.nextInt();
    int C = sc.nextInt();
    int D = sc.nextInt();
    
    int ans = Math.min(B, D) - Math.max(A, C);
    System.out.println(ans > 0 ? ans : 0);
  } main {
    Scanner sc = new Scanner(System.in);
    int A = sc.nextInt();
    int B = sc.nextInt();
    int C = sc.nextInt();
    int D = sc.nextInt();
    
    int ans = Math.min(B, D) - Math.max(A, C);
    System.out.println(ans > 0 ? ans : 0);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int A = sc.nextInt(); A sc.nextInt() sc.nextInt sc int B = sc.nextInt(); B sc.nextInt() sc.nextInt sc int C = sc.nextInt(); C sc.nextInt() sc.nextInt sc int D = sc.nextInt(); D sc.nextInt() sc.nextInt sc int ans = Math.min(B, D) - Math.max(A, C); ans Math.min(B, D) - Math.max(A, C) Math.min(B, D) Math.min Math B D Math.max(A, C) Math.max Math A C System.out.println(ans > 0 ? ans : 0) System.out.println System.out System System.out ans > 0 ? ans : 0 ans > 0 ans 0 ans 0 String[] args args public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int A = sc.nextInt();
    int B = sc.nextInt();
    int C = sc.nextInt();
    int D = sc.nextInt();
    
    int ans = Math.min(B, D) - Math.max(A, C);
    System.out.println(ans > 0 ? ans : 0);
  }
} public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int A = sc.nextInt();
    int B = sc.nextInt();
    int C = sc.nextInt();
    int D = sc.nextInt();
    
    int ans = Math.min(B, D) - Math.max(A, C);
    System.out.println(ans > 0 ? ans : 0);
  }
} Main
import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int A = sc.nextInt();
    int B = sc.nextInt();
    int C = sc.nextInt();
    int D = sc.nextInt();
    
    int ans = Math.min(B, D) - Math.max(A, C);
    System.out.println(ans > 0 ? ans : 0);
  }
}