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 max = (long)b*d;
    long[] cross = {(long)b*d,(long)a*c,(long)a*d,(long)b*c};


//積が最大になる掛け算を考える
//0<x,0<yのときはx,yは最大値
//x<0,y<0のときはx,yは最小値がベスト
//0<x,y<0のときは、xが最小値,yが最大値
//x<0,0<yのときは、xが最大値,yが最小値

    for(int i=0; i<cross.length; i++){
      if(max<cross[i]){
        max = cross[i];
      }
    }

    System.out.println(max);

	}
}

/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