import java.util.Scanner;

public class Main {

    Scanner scanner = new Scanner(System.in);

    public static void main(String[] args) {
        new Main().compute();
    }

    void compute() {
        int A = scanner.nextInt();
        int B = scanner.nextInt();
        int C = scanner.nextInt();
        int D = scanner.nextInt();
        int start = A > C ? A : C;
        int end = B < D ? B : D;
        System.out.println(end - start > 0 ? end - start : 0);
    }
}

/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