import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.StringTokenizer;
import java.io.BufferedReader;
import java.io.InputStreamReader;

public 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);
		TaskC solver = new TaskC();
		solver.solve(1, in, out);
		out.close();
	}

	static class TaskC {

		public void solve(int testNumber, InputReader in, PrintWriter out) {
			int a = in.nextInt();
			int b = in.nextInt();
			int c = in.nextInt();
			int d = in.nextInt();

			if (a > c) {
				int temp = a;
				a = c;
				c = temp;
				temp = b;
				b = d;
				d = temp;
			}
			int intersection = 0;
			if(b>c){
				if(b>d){
					intersection = d-c;
				}else{
					intersection = b-c;
				}
			}
			out.println(intersection);
		}

	}

	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());
		}

		public double nextFloat() {
			return Double.parseDouble(next());
		}

		public double nextDouble() {
			return Double.parseDouble(next());
		}

	}
} 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.ArrayList; ArrayList java.util import java.util.Arrays; Arrays java.util import java.util.StringTokenizer; StringTokenizer java.util import java.io.BufferedReader; BufferedReader java.io import java.io.InputStreamReader; InputStreamReader java.io public 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);
		TaskC solver = new TaskC();
		solver.solve(1, in, out);
		out.close();
	}

	static class TaskC {

		public void solve(int testNumber, InputReader in, PrintWriter out) {
			int a = in.nextInt();
			int b = in.nextInt();
			int c = in.nextInt();
			int d = in.nextInt();

			if (a > c) {
				int temp = a;
				a = c;
				c = temp;
				temp = b;
				b = d;
				d = temp;
			}
			int intersection = 0;
			if(b>c){
				if(b>d){
					intersection = d-c;
				}else{
					intersection = b-c;
				}
			}
			out.println(intersection);
		}

	}

	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());
		}

		public double nextFloat() {
			return Double.parseDouble(next());
		}

		public double nextDouble() {
			return Double.parseDouble(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);
		TaskC solver = new TaskC();
		solver.solve(1, in, out);
		out.close();
	} main {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		InputReader in = new InputReader(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		TaskC solver = new TaskC();
		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 InputReader in = new InputReader(inputStream); in new InputReader(inputStream) PrintWriter out = new PrintWriter(outputStream); out new PrintWriter(outputStream) TaskC solver = new TaskC(); solver new TaskC() solver.solve(1, in, out) solver.solve solver 1 in out out.close() out.close out String[] args args static class TaskC {

		public void solve(int testNumber, InputReader in, PrintWriter out) {
			int a = in.nextInt();
			int b = in.nextInt();
			int c = in.nextInt();
			int d = in.nextInt();

			if (a > c) {
				int temp = a;
				a = c;
				c = temp;
				temp = b;
				b = d;
				d = temp;
			}
			int intersection = 0;
			if(b>c){
				if(b>d){
					intersection = d-c;
				}else{
					intersection = b-c;
				}
			}
			out.println(intersection);
		}

	} TaskC public void solve(int testNumber, InputReader in, PrintWriter out) {
			int a = in.nextInt();
			int b = in.nextInt();
			int c = in.nextInt();
			int d = in.nextInt();

			if (a > c) {
				int temp = a;
				a = c;
				c = temp;
				temp = b;
				b = d;
				d = temp;
			}
			int intersection = 0;
			if(b>c){
				if(b>d){
					intersection = d-c;
				}else{
					intersection = b-c;
				}
			}
			out.println(intersection);
		} solve {
			int a = in.nextInt();
			int b = in.nextInt();
			int c = in.nextInt();
			int d = in.nextInt();

			if (a > c) {
				int temp = a;
				a = c;
				c = temp;
				temp = b;
				b = d;
				d = temp;
			}
			int intersection = 0;
			if(b>c){
				if(b>d){
					intersection = d-c;
				}else{
					intersection = b-c;
				}
			}
			out.println(intersection);
		} 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 (a > c) {
				int temp = a;
				a = c;
				c = temp;
				temp = b;
				b = d;
				d = temp;
			} a > c a c {
				int temp = a;
				a = c;
				c = temp;
				temp = b;
				b = d;
				d = temp;
			} int temp = a; temp a a = c a c c = temp c temp temp = b temp b b = d b d d = temp d temp int intersection = 0; intersection 0 if(b>c){
				if(b>d){
					intersection = d-c;
				}else{
					intersection = b-c;
				}
			} b>c b c {
				if(b>d){
					intersection = d-c;
				}else{
					intersection = b-c;
				}
			} if(b>d){
					intersection = d-c;
				}else{
					intersection = b-c;
				} b>d b d {
					intersection = d-c;
				} intersection = d-c intersection d-c d c {
					intersection = b-c;
				} intersection = b-c intersection b-c b c out.println(intersection) out.println out intersection int testNumber testNumber InputReader in in PrintWriter out out 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());
		}

		public double nextFloat() {
			return Double.parseDouble(next());
		}

		public double nextDouble() {
			return Double.parseDouble(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 public double nextFloat() {
			return Double.parseDouble(next());
		} nextFloat {
			return Double.parseDouble(next());
		} return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double next() next public double nextDouble() {
			return Double.parseDouble(next());
		} nextDouble {
			return Double.parseDouble(next());
		} return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double next() next public 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);
		TaskC solver = new TaskC();
		solver.solve(1, in, out);
		out.close();
	}

	static class TaskC {

		public void solve(int testNumber, InputReader in, PrintWriter out) {
			int a = in.nextInt();
			int b = in.nextInt();
			int c = in.nextInt();
			int d = in.nextInt();

			if (a > c) {
				int temp = a;
				a = c;
				c = temp;
				temp = b;
				b = d;
				d = temp;
			}
			int intersection = 0;
			if(b>c){
				if(b>d){
					intersection = d-c;
				}else{
					intersection = b-c;
				}
			}
			out.println(intersection);
		}

	}

	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());
		}

		public double nextFloat() {
			return Double.parseDouble(next());
		}

		public double nextDouble() {
			return Double.parseDouble(next());
		}

	}
} public 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);
		TaskC solver = new TaskC();
		solver.solve(1, in, out);
		out.close();
	}

	static class TaskC {

		public void solve(int testNumber, InputReader in, PrintWriter out) {
			int a = in.nextInt();
			int b = in.nextInt();
			int c = in.nextInt();
			int d = in.nextInt();

			if (a > c) {
				int temp = a;
				a = c;
				c = temp;
				temp = b;
				b = d;
				d = temp;
			}
			int intersection = 0;
			if(b>c){
				if(b>d){
					intersection = d-c;
				}else{
					intersection = b-c;
				}
			}
			out.println(intersection);
		}

	}

	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());
		}

		public double nextFloat() {
			return Double.parseDouble(next());
		}

		public double nextDouble() {
			return Double.parseDouble(next());
		}

	}
} Main
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.StringTokenizer;
import java.io.BufferedReader;
import java.io.InputStreamReader;

public 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);
		TaskC solver = new TaskC();
		solver.solve(1, in, out);
		out.close();
	}

	static class TaskC {

		public void solve(int testNumber, InputReader in, PrintWriter out) {
			int a = in.nextInt();
			int b = in.nextInt();
			int c = in.nextInt();
			int d = in.nextInt();

			if (a > c) {
				int temp = a;
				a = c;
				c = temp;
				temp = b;
				b = d;
				d = temp;
			}
			int intersection = 0;
			if(b>c){
				if(b>d){
					intersection = d-c;
				}else{
					intersection = b-c;
				}
			}
			out.println(intersection);
		}

	}

	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());
		}

		public double nextFloat() {
			return Double.parseDouble(next());
		}

		public double nextDouble() {
			return Double.parseDouble(next());
		}

	}
}