
import java.util.Arrays;
import java.util.Collections;
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

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 left = Math.max(a, c);
		int right = Math.min(b, d);
		
		if (right <= left) System.out.println(0);
		else System.out.println(right - left);
	}
}
/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