import java.util.*;

class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String[] abcd = scanner.nextLine().split(" ", 4);
        int a = Integer.parseInt(abcd[0]);
        int b = Integer.parseInt(abcd[1]);
        int c = Integer.parseInt(abcd[2]);
        int d = Integer.parseInt(abcd[3]);

        if (b <= c || d <= a) {
            System.out.println(0);
        } else {
            System.out.println(Math.min(b, d) - Math.max(c, a));
        }
    }
}

/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