import java.util.Scanner;

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 time = 0;
    int x = 0;
    int y = 0;
    x = Math.max(a,c);
    y = Math.min(b,d);
    if(y-x<0){
      System.out.println(0);
    }else{
      System.out.println(y-x);
    }
  }
} import java.util.Scanner; Scanner 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 time = 0;
    int x = 0;
    int y = 0;
    x = Math.max(a,c);
    y = Math.min(b,d);
    if(y-x<0){
      System.out.println(0);
    }else{
      System.out.println(y-x);
    }
  }
} 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 time = 0;
    int x = 0;
    int y = 0;
    x = Math.max(a,c);
    y = Math.min(b,d);
    if(y-x<0){
      System.out.println(0);
    }else{
      System.out.println(y-x);
    }
  } main {
    Scanner sc = new Scanner(System.in);
    int a = sc.nextInt();
    int b = sc.nextInt();
    int c = sc.nextInt();
    int d = sc.nextInt();
    int time = 0;
    int x = 0;
    int y = 0;
    x = Math.max(a,c);
    y = Math.min(b,d);
    if(y-x<0){
      System.out.println(0);
    }else{
      System.out.println(y-x);
    }
  } 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 time = 0; time 0 int x = 0; x 0 int y = 0; y 0 x = Math.max(a,c) x Math.max(a,c) Math.max Math a c y = Math.min(b,d) y Math.min(b,d) Math.min Math b d if(y-x<0){
      System.out.println(0);
    }else{
      System.out.println(y-x);
    } y-x<0 y-x y x 0 {
      System.out.println(0);
    } System.out.println(0) System.out.println System.out System System.out 0 {
      System.out.println(y-x);
    } System.out.println(y-x) System.out.println System.out System System.out y-x y x 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 time = 0;
    int x = 0;
    int y = 0;
    x = Math.max(a,c);
    y = Math.min(b,d);
    if(y-x<0){
      System.out.println(0);
    }else{
      System.out.println(y-x);
    }
  }
} 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 time = 0;
    int x = 0;
    int y = 0;
    x = Math.max(a,c);
    y = Math.min(b,d);
    if(y-x<0){
      System.out.println(0);
    }else{
      System.out.println(y-x);
    }
  }
} Main
import java.util.Scanner;

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 time = 0;
    int x = 0;
    int y = 0;
    x = Math.max(a,c);
    y = Math.min(b,d);
    if(y-x<0){
      System.out.println(0);
    }else{
      System.out.println(y-x);
    }
  }
}