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

/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