import java.util.Arrays;
import java.util.Scanner;

public class Main {
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        int[] nums = new int[4];
        for (int i = 0; i < nums.length; i++)
            nums[i] = sc.nextInt();
        if (nums[2] > nums[1] || nums[3] < nums[0]) {
            System.out.println(0);
            return;
        }
        Arrays.sort(nums);
        System.out.println(nums[2] - nums[1]);
    }
}

/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