import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner s = new Scanner(System.in);
			int a = s.nextInt();
			int b = s.nextInt();
			int c = s.nextInt();
			int d = s.nextInt();
			int start;
			int end;
			if(a < c){
				start = c;
       		}else{
                start = a;
        	}
      		if(b < d){
				end = b;
      		}else{
        		end = d;
      		}
      		if(start < end){
				System.out.println(end - start);
      		}else{
				System.out.println("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