import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.StringTokenizer;

 class Main {

    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        int a = in.nextInt();
        int b = in.nextInt();
        int c = in.nextInt();
        int d = in.nextInt();
        if (c > b) {
            System.out.println(0);
        } else if (a > d) {
            System.out.println(0);
        } else if (a < c) {
            System.out.println(Math.min(b, d) - c);
        } else {
            List<Integer> l = new ArrayList<>();
            l.add(a);
            l.add(b);
            l.add(c);
            l.add(d);
            Collections.sort(l);
            System.out.println(l.get(2) - l.get(1));
        }
    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

    }
} import java.io.BufferedReader; BufferedReader java.io import java.io.IOException; IOException java.io import java.io.InputStream; InputStream java.io import java.io.InputStreamReader; InputStreamReader java.io import java.io.OutputStream; OutputStream java.io import java.io.PrintWriter; PrintWriter java.io import java.util.ArrayList; ArrayList java.util import java.util.Arrays; Arrays java.util import java.util.Collections; Collections java.util import java.util.HashSet; HashSet java.util import java.util.List; List java.util import java.util.Set; Set java.util import java.util.StringTokenizer; StringTokenizer java.util class Main {

    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        int a = in.nextInt();
        int b = in.nextInt();
        int c = in.nextInt();
        int d = in.nextInt();
        if (c > b) {
            System.out.println(0);
        } else if (a > d) {
            System.out.println(0);
        } else if (a < c) {
            System.out.println(Math.min(b, d) - c);
        } else {
            List<Integer> l = new ArrayList<>();
            l.add(a);
            l.add(b);
            l.add(c);
            l.add(d);
            Collections.sort(l);
            System.out.println(l.get(2) - l.get(1));
        }
    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

    }
} Main public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        int a = in.nextInt();
        int b = in.nextInt();
        int c = in.nextInt();
        int d = in.nextInt();
        if (c > b) {
            System.out.println(0);
        } else if (a > d) {
            System.out.println(0);
        } else if (a < c) {
            System.out.println(Math.min(b, d) - c);
        } else {
            List<Integer> l = new ArrayList<>();
            l.add(a);
            l.add(b);
            l.add(c);
            l.add(d);
            Collections.sort(l);
            System.out.println(l.get(2) - l.get(1));
        }
    } main {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        int a = in.nextInt();
        int b = in.nextInt();
        int c = in.nextInt();
        int d = in.nextInt();
        if (c > b) {
            System.out.println(0);
        } else if (a > d) {
            System.out.println(0);
        } else if (a < c) {
            System.out.println(Math.min(b, d) - c);
        } else {
            List<Integer> l = new ArrayList<>();
            l.add(a);
            l.add(b);
            l.add(c);
            l.add(d);
            Collections.sort(l);
            System.out.println(l.get(2) - l.get(1));
        }
    } InputStream inputStream = System.in; inputStream System.in System System.in OutputStream outputStream = System.out; outputStream System.out System System.out InputReader in = new InputReader(inputStream); in new InputReader(inputStream) PrintWriter out = new PrintWriter(outputStream); out new PrintWriter(outputStream) int a = in.nextInt(); a in.nextInt() in.nextInt in int b = in.nextInt(); b in.nextInt() in.nextInt in int c = in.nextInt(); c in.nextInt() in.nextInt in int d = in.nextInt(); d in.nextInt() in.nextInt in if (c > b) {
            System.out.println(0);
        } else if (a > d) {
            System.out.println(0);
        } else if (a < c) {
            System.out.println(Math.min(b, d) - c);
        } else {
            List<Integer> l = new ArrayList<>();
            l.add(a);
            l.add(b);
            l.add(c);
            l.add(d);
            Collections.sort(l);
            System.out.println(l.get(2) - l.get(1));
        } c > b c b {
            System.out.println(0);
        } System.out.println(0) System.out.println System.out System System.out 0 if (a > d) {
            System.out.println(0);
        } else if (a < c) {
            System.out.println(Math.min(b, d) - c);
        } else {
            List<Integer> l = new ArrayList<>();
            l.add(a);
            l.add(b);
            l.add(c);
            l.add(d);
            Collections.sort(l);
            System.out.println(l.get(2) - l.get(1));
        } a > d a d {
            System.out.println(0);
        } System.out.println(0) System.out.println System.out System System.out 0 if (a < c) {
            System.out.println(Math.min(b, d) - c);
        } else {
            List<Integer> l = new ArrayList<>();
            l.add(a);
            l.add(b);
            l.add(c);
            l.add(d);
            Collections.sort(l);
            System.out.println(l.get(2) - l.get(1));
        } a < c a c {
            System.out.println(Math.min(b, d) - c);
        } System.out.println(Math.min(b, d) - c) System.out.println System.out System System.out Math.min(b, d) - c Math.min(b, d) Math.min Math b d c {
            List<Integer> l = new ArrayList<>();
            l.add(a);
            l.add(b);
            l.add(c);
            l.add(d);
            Collections.sort(l);
            System.out.println(l.get(2) - l.get(1));
        } List<Integer> l = new ArrayList<>(); l new ArrayList<>() l.add(a) l.add l a l.add(b) l.add l b l.add(c) l.add l c l.add(d) l.add l d Collections.sort(l) Collections.sort Collections l System.out.println(l.get(2) - l.get(1)) System.out.println System.out System System.out l.get(2) - l.get(1) l.get(2) l.get l 2 l.get(1) l.get l 1 String[] args args static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

    } InputReader public BufferedReader reader; reader public StringTokenizer tokenizer; tokenizer public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        } InputReader {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        } reader = new BufferedReader(new InputStreamReader(stream), 32768) reader new BufferedReader(new InputStreamReader(stream), 32768) tokenizer = null tokenizer null InputStream stream stream public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        } next {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        } while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            } tokenizer == null || !tokenizer.hasMoreTokens() tokenizer == null tokenizer null !tokenizer.hasMoreTokens() tokenizer.hasMoreTokens() tokenizer.hasMoreTokens tokenizer {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            } try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                } catch (IOException e) {
                    throw new RuntimeException(e);
                } IOException e {
                    throw new RuntimeException(e);
                } throw new RuntimeException(e); new RuntimeException(e) {
                    tokenizer = new StringTokenizer(reader.readLine());
                } tokenizer = new StringTokenizer(reader.readLine()) tokenizer new StringTokenizer(reader.readLine()) return tokenizer.nextToken(); tokenizer.nextToken() tokenizer.nextToken tokenizer public int nextInt() {
            return Integer.parseInt(next());
        } nextInt {
            return Integer.parseInt(next());
        } return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next public long nextLong() {
            return Long.parseLong(next());
        } nextLong {
            return Long.parseLong(next());
        } return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.StringTokenizer;

 class Main {

    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        int a = in.nextInt();
        int b = in.nextInt();
        int c = in.nextInt();
        int d = in.nextInt();
        if (c > b) {
            System.out.println(0);
        } else if (a > d) {
            System.out.println(0);
        } else if (a < c) {
            System.out.println(Math.min(b, d) - c);
        } else {
            List<Integer> l = new ArrayList<>();
            l.add(a);
            l.add(b);
            l.add(c);
            l.add(d);
            Collections.sort(l);
            System.out.println(l.get(2) - l.get(1));
        }
    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

    }
}
