import java.util.Scanner;

public class Main {

    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 start = 0;
        int end = 100;
        int res = 0;

        if(a <= c){
            start = c;
        } else {
            start = a;
        }

        if(b <= d){
            end = b;
        } else {
            end = d;
        }

        res = end - start;
        if(res < 0){
            res = 0;
        }

        System.out.println(res);
        sc.close();
    }

}
/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