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

public class Main {

	public static void main(String[] args) throws IOException {

		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		StringTokenizer st = new StringTokenizer(br.readLine(), " ");
		
		long a = Long.parseLong(st.nextToken());
		long b = Long.parseLong(st.nextToken());
		long c = Long.parseLong(st.nextToken());
		long d = Long.parseLong(st.nextToken());

		long ans = Math.max(a * c, a * d);
		ans = Math.max( ans, Math.max(b*c, b * d));
		
		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