import java.util.Scanner;

public class Main {

    public static void main (String [] args){
        Scanner sc = new Scanner(System.in);
        int Alice_start = sc.nextInt();
        int Alice_end =sc.nextInt();
        int Bob_start =sc.nextInt();
        int Bob_end =sc.nextInt();
        int low = Math.max(Alice_start,Bob_start);
        int upp = Math.min(Alice_end,Bob_end);
        System.out.println(Math.max(0,upp-low));
    }
}
/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