import java.util.*;

class Main{
    final static long mod = 1000000007;
    //
    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 e = Math.min(b,d) - Math.max(a,c);
        if(e >= 0) System.out.println(e);
        else System.out.println(0);
    }
} import java.util.*; util.* java class Main{
    final static long mod = 1000000007;
    //
    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 e = Math.min(b,d) - Math.max(a,c);
        if(e >= 0) System.out.println(e);
        else System.out.println(0);
    }
} Main final static long mod = 1000000007; mod 1000000007 //
    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 e = Math.min(b,d) - Math.max(a,c);
        if(e >= 0) System.out.println(e);
        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 e = Math.min(b,d) - Math.max(a,c);
        if(e >= 0) System.out.println(e);
        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 e = Math.min(b,d) - Math.max(a,c); e Math.min(b,d) - Math.max(a,c) Math.min(b,d) Math.min Math b d Math.max(a,c) Math.max Math a c if(e >= 0) System.out.println(e);
        else System.out.println(0); e >= 0 e 0 System.out.println(e) System.out.println System.out System System.out e System.out.println(0) System.out.println System.out System System.out 0 String[] args args
import java.util.*;

class Main{
    final static long mod = 1000000007;
    //
    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 e = Math.min(b,d) - Math.max(a,c);
        if(e >= 0) System.out.println(e);
        else System.out.println(0);
    }
}