import java.util.Scanner;

public class Main {
 
	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);
		while(input.hasNext()){
			int A = input.nextInt();
			int B = input.nextInt();
			int C = input.nextInt();
			int D = input.nextInt();
			if(A > D || C > B){
				System.out.println("0");
			} else {
				System.out.println(Math.min(B, D) - Math.max(A, C));
			}
		}
	}
  
}
/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