import java.io.IOException;

import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Main {
    public static void main(String[] args) throws IOException {
        try (
            BufferedReader reader = new BufferedReader(
                new InputStreamReader(System.in))) {
            final String s = reader.readLine();

            final String[] sl = s.split(" ");
            int A = Integer.parseInt(sl[0]);
            int B = Integer.parseInt(sl[1]);
            int C = Integer.parseInt(sl[2]);
            int D = Integer.parseInt(sl[3]);

            int ans = 0;
            if (A <= C && C <= B) ans = Math.min(B, D) - C;
            else if (A <= D && D <= B) ans = D - Math.max(A, C);
            else if (C < A && B < D) ans = B - A;

            System.out.println(ans);
        }
    }
}

/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