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 count = 0;
        for(int i = 0;i<=100;i++){
            if(Math.max(a,c) <= i && Math.min(b,d) > i){
                count++;
            }
        }
        System.out.println(count);
    }
} 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 count = 0;
        for(int i = 0;i<=100;i++){
            if(Math.max(a,c) <= i && Math.min(b,d) > i){
                count++;
            }
        }
        System.out.println(count);
    }
} 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 count = 0;
        for(int i = 0;i<=100;i++){
            if(Math.max(a,c) <= i && Math.min(b,d) > i){
                count++;
            }
        }
        System.out.println(count);
    } main {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();
        int d = sc.nextInt();
        int count = 0;
        for(int i = 0;i<=100;i++){
            if(Math.max(a,c) <= i && Math.min(b,d) > i){
                count++;
            }
        }
        System.out.println(count);
    } 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 count = 0; count 0 for(int i = 0;i<=100;i++){
            if(Math.max(a,c) <= i && Math.min(b,d) > i){
                count++;
            }
        } int i = 0; int i = 0; i 0 i<=100 i 100 i++ i++ i {
            if(Math.max(a,c) <= i && Math.min(b,d) > i){
                count++;
            }
        } {
            if(Math.max(a,c) <= i && Math.min(b,d) > i){
                count++;
            }
        } if(Math.max(a,c) <= i && Math.min(b,d) > i){
                count++;
            } Math.max(a,c) <= i && Math.min(b,d) > i Math.max(a,c) <= i Math.max(a,c) Math.max Math a c i Math.min(b,d) > i Math.min(b,d) Math.min Math b d i {
                count++;
            } count++ count System.out.println(count) System.out.println System.out System System.out count 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 count = 0;
        for(int i = 0;i<=100;i++){
            if(Math.max(a,c) <= i && Math.min(b,d) > i){
                count++;
            }
        }
        System.out.println(count);
    }
} 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 count = 0;
        for(int i = 0;i<=100;i++){
            if(Math.max(a,c) <= i && Math.min(b,d) > i){
                count++;
            }
        }
        System.out.println(count);
    }
} 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 count = 0;
        for(int i = 0;i<=100;i++){
            if(Math.max(a,c) <= i && Math.min(b,d) > i){
                count++;
            }
        }
        System.out.println(count);
    }
}