import java.util.*;

class Main {
  public static void main(String[] args) {
      Scanner sc = new Scanner(System.in);
      long a = sc.nextInt();
      long b = sc.nextInt();
      long c = sc.nextInt();
      long d = sc.nextInt();
      
      long currentMax = -9223372036854775807L;

      if (a*c > currentMax) {
        currentMax = a*c;
      }

      if (a*d > currentMax) {
        currentMax = a*d;
      }

      if (b*c > currentMax) {
        currentMax = b*c;
      }

      if (b*d > currentMax) {
        currentMax = b*d;
      }

      System.out.println(currentMax);
    }
}
/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