import java.util.Scanner;
import java.util.Arrays;
public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int[] a = new int [2];
        int[] b = new int [2];
        for(int i = 0;i < 2;i++){
            a[i] = sc.nextInt();
        }
        for(int i = 0;i < 2;i++){
            b[i] = sc.nextInt();
        }
        int ans = Math.min(a[1],b[1]) - Math.max(a[0],b[0]);
        if(ans <= 0){
            System.out.println(0);
            return;
        }
        System.out.println(ans);
    }
}

/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