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 sm=c,bg=d;
        if(a>c){
            sm=a;
        }
        if(b<d){
            bg=b;
        }
        if(bg>sm){
            System.out.println(bg-sm);

        }
        else{
            System.out.println(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 sm=c,bg=d;
        if(a>c){
            sm=a;
        }
        if(b<d){
            bg=b;
        }
        if(bg>sm){
            System.out.println(bg-sm);

        }
        else{
            System.out.println(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 sm=c,bg=d;
        if(a>c){
            sm=a;
        }
        if(b<d){
            bg=b;
        }
        if(bg>sm){
            System.out.println(bg-sm);

        }
        else{
            System.out.println(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 sm=c,bg=d;
        if(a>c){
            sm=a;
        }
        if(b<d){
            bg=b;
        }
        if(bg>sm){
            System.out.println(bg-sm);

        }
        else{
            System.out.println(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 sm=c sm c bg=d; bg d if(a>c){
            sm=a;
        } a>c a c {
            sm=a;
        } sm=a sm a if(b<d){
            bg=b;
        } b<d b d {
            bg=b;
        } bg=b bg b if(bg>sm){
            System.out.println(bg-sm);

        }
        else{
            System.out.println(0);
        } bg>sm bg sm {
            System.out.println(bg-sm);

        } System.out.println(bg-sm) System.out.println System.out System System.out bg-sm bg sm {
            System.out.println(0);
        } System.out.println(0) System.out.println System.out System System.out 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 sm=c,bg=d;
        if(a>c){
            sm=a;
        }
        if(b<d){
            bg=b;
        }
        if(bg>sm){
            System.out.println(bg-sm);

        }
        else{
            System.out.println(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 sm=c,bg=d;
        if(a>c){
            sm=a;
        }
        if(b<d){
            bg=b;
        }
        if(bg>sm){
            System.out.println(bg-sm);

        }
        else{
            System.out.println(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 sm=c,bg=d;
        if(a>c){
            sm=a;
        }
        if(b<d){
            bg=b;
        }
        if(bg>sm){
            System.out.println(bg-sm);

        }
        else{
            System.out.println(0);
        }
       
    }
}