import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        B solver = new B();
        solver.solve(1, in, out);
        out.close();
    }

    static class B {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());
            int c = Integer.parseInt(in.next());
            int d = Integer.parseInt(in.next());
            int ans = Math.max(0, Math.min(b, d) - Math.max(a, c));

            // 出力
            out.println(ans);

        }

    }
}
 import java.io.OutputStream; OutputStream java.io import java.io.IOException; IOException java.io import java.io.InputStream; InputStream java.io import java.io.PrintWriter; PrintWriter java.io import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        B solver = new B();
        solver.solve(1, in, out);
        out.close();
    }

    static class B {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());
            int c = Integer.parseInt(in.next());
            int d = Integer.parseInt(in.next());
            int ans = Math.max(0, Math.min(b, d) - Math.max(a, c));

            // 出力
            out.println(ans);

        }

    }
} Main public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        B solver = new B();
        solver.solve(1, in, out);
        out.close();
    } main {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        B solver = new B();
        solver.solve(1, in, out);
        out.close();
    } InputStream inputStream = System.in; inputStream System.in System System.in OutputStream outputStream = System.out; outputStream System.out System System.out Scanner in = new Scanner(inputStream); in new Scanner(inputStream) PrintWriter out = new PrintWriter(outputStream); out new PrintWriter(outputStream) B solver = new B(); solver new B() solver.solve(1, in, out) solver.solve solver 1 in out out.close() out.close out String[] args args static class B {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());
            int c = Integer.parseInt(in.next());
            int d = Integer.parseInt(in.next());
            int ans = Math.max(0, Math.min(b, d) - Math.max(a, c));

            // 出力
            out.println(ans);

        }

    } B public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());
            int c = Integer.parseInt(in.next());
            int d = Integer.parseInt(in.next());
            int ans = Math.max(0, Math.min(b, d) - Math.max(a, c));

            // 出力
            out.println(ans);

        } solve {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());
            int c = Integer.parseInt(in.next());
            int d = Integer.parseInt(in.next());
            int ans = Math.max(0, Math.min(b, d) - Math.max(a, c));

            // 出力
            out.println(ans);

        } int a = Integer.parseInt(in.next()); a Integer.parseInt(in.next()) Integer.parseInt Integer in.next() in.next in int b = Integer.parseInt(in.next()); b Integer.parseInt(in.next()) Integer.parseInt Integer in.next() in.next in int c = Integer.parseInt(in.next()); c Integer.parseInt(in.next()) Integer.parseInt Integer in.next() in.next in int d = Integer.parseInt(in.next()); d Integer.parseInt(in.next()) Integer.parseInt Integer in.next() in.next in 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 int testNumber testNumber Scanner in in PrintWriter out out public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        B solver = new B();
        solver.solve(1, in, out);
        out.close();
    }

    static class B {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());
            int c = Integer.parseInt(in.next());
            int d = Integer.parseInt(in.next());
            int ans = Math.max(0, Math.min(b, d) - Math.max(a, c));

            // 出力
            out.println(ans);

        }

    }
} public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        B solver = new B();
        solver.solve(1, in, out);
        out.close();
    }

    static class B {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());
            int c = Integer.parseInt(in.next());
            int d = Integer.parseInt(in.next());
            int ans = Math.max(0, Math.min(b, d) - Math.max(a, c));

            // 出力
            out.println(ans);

        }

    }
} Main
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        B solver = new B();
        solver.solve(1, in, out);
        out.close();
    }

    static class B {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());
            int c = Integer.parseInt(in.next());
            int d = Integer.parseInt(in.next());
            int ans = Math.max(0, Math.min(b, d) - Math.max(a, c));

            // 出力
            out.println(ans);

        }

    }
}

