import java.util.*;

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();
      
      long tmp1 = (long)a*(long)c;
      long tmp2 = (long)a*(long)d;
      long tmp3 = (long)b*(long)c;
      long tmp4 = (long)b*(long)d;

      // tmp1のチェック
      if(((tmp1>tmp2)|| (tmp1==tmp2)) &&((tmp1>tmp3) || (tmp1==tmp3)) && ((tmp1>tmp4) || (tmp1==tmp4))){

            System.out.println(tmp1);
      // tmp2のチェック
      }else if (((tmp2>tmp1) || (tmp2==tmp1)) && ((tmp2>tmp3) || (tmp2==tmp3)) && ((tmp2>tmp4) || (tmp2==tmp4))){

            System.out.println(tmp2);
      // tmp3のチェック  
      }else if (((tmp3>tmp1) || (tmp3==tmp1)) && ((tmp3>tmp2) || (tmp3==tmp2)) && ((tmp3>tmp4) || (tmp3==tmp4))){

            System.out.println(tmp3);
      }else if (((tmp4>tmp1) || (tmp4==tmp1)) && ((tmp4>tmp2) || (tmp4==tmp2)) && ((tmp4>tmp3) || (tmp4==tmp3))){

            System.out.println(tmp4);
      }
    }
}
/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