import java.util.*;
import java.io.*;

public class Main {
    public static void main(String[] args) throws Exception {

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
        
        String[] input = br.readLine().split(" ");
        int a = Integer.parseInt(input[0]);
        int b = Integer.parseInt(input[1]);
        int c = Integer.parseInt(input[2]);
        int d = Integer.parseInt(input[3]);
        
        int ans = Math.max(0, Math.min(b, d) - Math.max(a, c));
        
        out.println(ans);
        out.close();
        
    }
} import java.util.*; util.* java import java.io.*; io.* java public class Main {
    public static void main(String[] args) throws Exception {

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
        
        String[] input = br.readLine().split(" ");
        int a = Integer.parseInt(input[0]);
        int b = Integer.parseInt(input[1]);
        int c = Integer.parseInt(input[2]);
        int d = Integer.parseInt(input[3]);
        
        int ans = Math.max(0, Math.min(b, d) - Math.max(a, c));
        
        out.println(ans);
        out.close();
        
    }
} Main public static void main(String[] args) throws Exception {

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
        
        String[] input = br.readLine().split(" ");
        int a = Integer.parseInt(input[0]);
        int b = Integer.parseInt(input[1]);
        int c = Integer.parseInt(input[2]);
        int d = Integer.parseInt(input[3]);
        
        int ans = Math.max(0, Math.min(b, d) - Math.max(a, c));
        
        out.println(ans);
        out.close();
        
    } main {

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
        
        String[] input = br.readLine().split(" ");
        int a = Integer.parseInt(input[0]);
        int b = Integer.parseInt(input[1]);
        int c = Integer.parseInt(input[2]);
        int d = Integer.parseInt(input[3]);
        
        int ans = Math.max(0, Math.min(b, d) - Math.max(a, c));
        
        out.println(ans);
        out.close();
        
    } BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); br new BufferedReader(new InputStreamReader(System.in)) PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out)); out new PrintWriter(new OutputStreamWriter(System.out)) String[] input = br.readLine().split(" "); input br.readLine().split(" ") br.readLine().split br.readLine() br.readLine br " " int a = Integer.parseInt(input[0]); a Integer.parseInt(input[0]) Integer.parseInt Integer input[0] input 0 int b = Integer.parseInt(input[1]); b Integer.parseInt(input[1]) Integer.parseInt Integer input[1] input 1 int c = Integer.parseInt(input[2]); c Integer.parseInt(input[2]) Integer.parseInt Integer input[2] input 2 int d = Integer.parseInt(input[3]); d Integer.parseInt(input[3]) Integer.parseInt Integer input[3] input 3 int ans = Math.max(0, Math.min(b, d) - Math.max(a, c)); ans Math.max(0, Math.min(b, d) - Math.max(a, c)) Math.max Math 0 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 out.println(ans) out.println out ans out.close() out.close out String[] args args public class Main {
    public static void main(String[] args) throws Exception {

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
        
        String[] input = br.readLine().split(" ");
        int a = Integer.parseInt(input[0]);
        int b = Integer.parseInt(input[1]);
        int c = Integer.parseInt(input[2]);
        int d = Integer.parseInt(input[3]);
        
        int ans = Math.max(0, Math.min(b, d) - Math.max(a, c));
        
        out.println(ans);
        out.close();
        
    }
} public class Main {
    public static void main(String[] args) throws Exception {

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
        
        String[] input = br.readLine().split(" ");
        int a = Integer.parseInt(input[0]);
        int b = Integer.parseInt(input[1]);
        int c = Integer.parseInt(input[2]);
        int d = Integer.parseInt(input[3]);
        
        int ans = Math.max(0, Math.min(b, d) - Math.max(a, c));
        
        out.println(ans);
        out.close();
        
    }
} Main
import java.util.*;
import java.io.*;

public class Main {
    public static void main(String[] args) throws Exception {

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
        
        String[] input = br.readLine().split(" ");
        int a = Integer.parseInt(input[0]);
        int b = Integer.parseInt(input[1]);
        int c = Integer.parseInt(input[2]);
        int d = Integer.parseInt(input[3]);
        
        int ans = Math.max(0, Math.min(b, d) - Math.max(a, c));
        
        out.println(ans);
        out.close();
        
    }
}