import java.util.*;
class Main{
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		long[] nums = new long[4];
		for(int i = 0; i < 4; i++) {
			nums[i] = scanner.nextInt();
		}
		long result = nums[0] * nums[2];
		if(result < nums[0]*nums[3])result = nums[0]*nums[3];
		if(result < nums[1]*nums[2])result = nums[1]*nums[2];
		if(result < nums[1]*nums[3])result = nums[1]*nums[3];
		System.out.println(result);
		scanner.close();
	}
}
/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