import java.util.*;
import java.util.stream.IntStream;

public class Main {

    public static boolean found = false;

    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);

        int a = sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();
        int d = sc.nextInt();

        int minSec = Integer.MAX_VALUE;
        int maxSec = 0;

        for (int i = 0; i < 101; i++) {
            boolean alice = (a <= i && i <= b);
            boolean bob = (c <= i && i <= d);

            if (alice && bob) {
                maxSec = Math.max(maxSec, i);
                minSec = Math.min(minSec, i);
            }
        }

        if (minSec == Integer.MAX_VALUE) {
            System.out.println("0");
        } else {
            System.out.println(maxSec - minSec);
        }
    }

}
/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