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 startMax = Math.max(a, c);
    int stopMin = Math.min(b,d);
    if(startMax > stopMin) {
      System.out.println(0);
    }else {
      System.out.println(stopMin - startMax);
    }
  }
} 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 startMax = Math.max(a, c);
    int stopMin = Math.min(b,d);
    if(startMax > stopMin) {
      System.out.println(0);
    }else {
      System.out.println(stopMin - startMax);
    }
  }
} 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 startMax = Math.max(a, c);
    int stopMin = Math.min(b,d);
    if(startMax > stopMin) {
      System.out.println(0);
    }else {
      System.out.println(stopMin - startMax);
    }
  } main {
    Scanner sc = new Scanner(System.in);
    int a = sc.nextInt();
    int b = sc.nextInt();
    int c = sc.nextInt();
    int d = sc.nextInt();

    int startMax = Math.max(a, c);
    int stopMin = Math.min(b,d);
    if(startMax > stopMin) {
      System.out.println(0);
    }else {
      System.out.println(stopMin - startMax);
    }
  } 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 startMax = Math.max(a, c); startMax Math.max(a, c) Math.max Math a c int stopMin = Math.min(b,d); stopMin Math.min(b,d) Math.min Math b d if(startMax > stopMin) {
      System.out.println(0);
    }else {
      System.out.println(stopMin - startMax);
    } startMax > stopMin startMax stopMin {
      System.out.println(0);
    } System.out.println(0) System.out.println System.out System System.out 0 {
      System.out.println(stopMin - startMax);
    } System.out.println(stopMin - startMax) System.out.println System.out System System.out stopMin - startMax stopMin startMax 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 startMax = Math.max(a, c);
    int stopMin = Math.min(b,d);
    if(startMax > stopMin) {
      System.out.println(0);
    }else {
      System.out.println(stopMin - startMax);
    }
  }
} 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 startMax = Math.max(a, c);
    int stopMin = Math.min(b,d);
    if(startMax > stopMin) {
      System.out.println(0);
    }else {
      System.out.println(stopMin - startMax);
    }
  }
} 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 startMax = Math.max(a, c);
    int stopMin = Math.min(b,d);
    if(startMax > stopMin) {
      System.out.println(0);
    }else {
      System.out.println(stopMin - startMax);
    }
  }
}
