
import java.util.Scanner;
 
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 ans = 0;
		if(B <= C || D <= A) {
			ans = 0;
		} else if(C <= A && A <= D && D <= B){
			ans = D - A;
		} else if(C <= A && B <= D) {
			ans = B - A;
		} else if(A <= C && C <= B && D <= B) {
			ans = D - C;
		} else if(A <= C && C <= B && B <= D) {
			ans = B - C;
		}
		System.out.println(ans);
	}
}
/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