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();

    if(A<=C && B<=C){
        System.out.println("0");
    }else if(A<=C && B<=D){
        System.out.println(B-C);
    }else if(A<=C && B>D){
        System.out.println(D-C);
    }else if(A>C && D<=A){
        System.out.println("0");
    }else if(A>C && B>=D){
        System.out.println(D-A);
    }else{
        System.out.println(B-A);
    }
    }
} 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();

    if(A<=C && B<=C){
        System.out.println("0");
    }else if(A<=C && B<=D){
        System.out.println(B-C);
    }else if(A<=C && B>D){
        System.out.println(D-C);
    }else if(A>C && D<=A){
        System.out.println("0");
    }else if(A>C && B>=D){
        System.out.println(D-A);
    }else{
        System.out.println(B-A);
    }
    }
} 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();

    if(A<=C && B<=C){
        System.out.println("0");
    }else if(A<=C && B<=D){
        System.out.println(B-C);
    }else if(A<=C && B>D){
        System.out.println(D-C);
    }else if(A>C && D<=A){
        System.out.println("0");
    }else if(A>C && B>=D){
        System.out.println(D-A);
    }else{
        System.out.println(B-A);
    }
    } main {
    
    Scanner sc = new Scanner(System.in);
    int A = sc.nextInt();
    int B = sc.nextInt();
    int C = sc.nextInt();
    int D = sc.nextInt();

    if(A<=C && B<=C){
        System.out.println("0");
    }else if(A<=C && B<=D){
        System.out.println(B-C);
    }else if(A<=C && B>D){
        System.out.println(D-C);
    }else if(A>C && D<=A){
        System.out.println("0");
    }else if(A>C && B>=D){
        System.out.println(D-A);
    }else{
        System.out.println(B-A);
    }
    } 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 if(A<=C && B<=C){
        System.out.println("0");
    }else if(A<=C && B<=D){
        System.out.println(B-C);
    }else if(A<=C && B>D){
        System.out.println(D-C);
    }else if(A>C && D<=A){
        System.out.println("0");
    }else if(A>C && B>=D){
        System.out.println(D-A);
    }else{
        System.out.println(B-A);
    } A<=C && B<=C A<=C A C B<=C B C {
        System.out.println("0");
    } System.out.println("0") System.out.println System.out System System.out "0" if(A<=C && B<=D){
        System.out.println(B-C);
    }else if(A<=C && B>D){
        System.out.println(D-C);
    }else if(A>C && D<=A){
        System.out.println("0");
    }else if(A>C && B>=D){
        System.out.println(D-A);
    }else{
        System.out.println(B-A);
    } A<=C && B<=D A<=C A C B<=D B D {
        System.out.println(B-C);
    } System.out.println(B-C) System.out.println System.out System System.out B-C B C if(A<=C && B>D){
        System.out.println(D-C);
    }else if(A>C && D<=A){
        System.out.println("0");
    }else if(A>C && B>=D){
        System.out.println(D-A);
    }else{
        System.out.println(B-A);
    } A<=C && B>D A<=C A C B>D B D {
        System.out.println(D-C);
    } System.out.println(D-C) System.out.println System.out System System.out D-C D C if(A>C && D<=A){
        System.out.println("0");
    }else if(A>C && B>=D){
        System.out.println(D-A);
    }else{
        System.out.println(B-A);
    } A>C && D<=A A>C A C D<=A D A {
        System.out.println("0");
    } System.out.println("0") System.out.println System.out System System.out "0" if(A>C && B>=D){
        System.out.println(D-A);
    }else{
        System.out.println(B-A);
    } A>C && B>=D A>C A C B>=D B D {
        System.out.println(D-A);
    } System.out.println(D-A) System.out.println System.out System System.out D-A D A {
        System.out.println(B-A);
    } System.out.println(B-A) System.out.println System.out System System.out B-A B A 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();

    if(A<=C && B<=C){
        System.out.println("0");
    }else if(A<=C && B<=D){
        System.out.println(B-C);
    }else if(A<=C && B>D){
        System.out.println(D-C);
    }else if(A>C && D<=A){
        System.out.println("0");
    }else if(A>C && B>=D){
        System.out.println(D-A);
    }else{
        System.out.println(B-A);
    }
    }
} 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();

    if(A<=C && B<=C){
        System.out.println("0");
    }else if(A<=C && B<=D){
        System.out.println(B-C);
    }else if(A<=C && B>D){
        System.out.println(D-C);
    }else if(A>C && D<=A){
        System.out.println("0");
    }else if(A>C && B>=D){
        System.out.println(D-A);
    }else{
        System.out.println(B-A);
    }
    }
} 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();

    if(A<=C && B<=C){
        System.out.println("0");
    }else if(A<=C && B<=D){
        System.out.println(B-C);
    }else if(A<=C && B>D){
        System.out.println(D-C);
    }else if(A>C && D<=A){
        System.out.println("0");
    }else if(A>C && B>=D){
        System.out.println(D-A);
    }else{
        System.out.println(B-A);
    }
    }
}
