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

public class Main {

	public static void main(String args[]) {
		ConsoleScanner cin = new ConsoleScanner();
		PrintWriter cout = new PrintWriter(System.out);
		solve(cin, cout);
		cout.flush();
	}

	static long now() {
		return System.currentTimeMillis();
	}

	static void trace(Object... objects) {
		assert null != System.out.format("trace:%s\n", Arrays.deepToString(objects));
	}

	private static void solve(ConsoleScanner cin, PrintWriter cout) {
		// assert solve(1) == 1;
		int a = cin.nextInt();
		int b = cin.nextInt();
		int c = cin.nextInt();
		int d = cin.nextInt();

		long start = now();

		int ans = solve(a, b, c, d);

		cout.println(ans);
		trace("elapsed", now() - start);
	}

	private static int solve(int a, int b, int c, int d) {
		int s = Math.max(a, c);
		int e = Math.min(b, d);
		int ans = Math.max(0, e - s);
		return ans;
	}

	static class ConsoleScanner {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st = new StringTokenizer("");

		String next() {
			try {
				while (!st.hasMoreElements())
					st = new StringTokenizer(br.readLine());
				return st.nextToken();
			} catch (IOException e) {
				throw new AssertionError(e);
			}
		}

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

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

}

/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz