import java.util.*;

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();

    if(A<=C && B<=C){
        System.out.println("0");
    }else if(A<=C && B<=D){
        System.out.println(B-C);
    }else if(A<=C && B>D){
        System.out.println(D-C);
    }else if(A>C && D<=A){
        System.out.println("0");
    }else if(A>C && B>=D){
        System.out.println(D-A);
    }else{
        System.out.println(B-A);
    }
    }
}

/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