import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;


public class Main {

	/**
	 * @param args
	 * @throws IOException 
	 */
	public static void main(String[] args) throws IOException {
		// TODO Auto-generated method stub
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String[] strArray = br.readLine().split(" ");
		
		int[] input = new int [4];
		
		for(int i = 0; i < 4; i++){
			input[i] = Integer.parseInt(strArray[i]);
		}
		
		int on = Math.max(input[0], input[2]);
		int off = Math.min(input[1], input[3]);
//		System.out.println("on "+on+" off "+off);
		
		System.out.println(Math.max(off-on, 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