import java.util.*;
public class Main {
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		int x = 0,y = 0;
		if(a > c) {
			y = a;
			a = c;
			c = y;
			y = b;
			b = d;
			d = y;
		}
		if(b < c) {
			System.out.println(x);
		}else if(b < d ){
			x = (b - c);
			System.out.println(x);
		}else{
			x = (d - c);
			System.out.println(x);
		}
	}
}


/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