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

public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int num[] = new int[4];

        for(int i = 0; i < 4; i++){
            num[i] = sc.nextInt();
        }

        if(num[0] <= num[2] && num[2] <= num[1] && num[1] <= num[3]){
            System.out.print(num[1] -num[2]);
        } else if(num[0] <= num[2] && num[2] <= num[3] && num[3] <= num[1]){
            System.out.print(num[3] - num[2]);
        } else if(num[2] <= num[0] && num[0] <= num[3] && num[3] <= num[1]){
            System.out.print(num[3] - num[0]);
        } else if(num[2] <= num[0] && num[0] <= num[1] && num[1] <= num[3]){
            System.out.print(num[1] - num[0]);
        } else{
            System.out.print(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