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);

	}
} import java.util.*; util.* java 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);

	}
} 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);

	} main {
		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);

	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int a = sc.nextInt(); a sc.nextInt() sc.nextInt sc int b = sc.nextInt(); b sc.nextInt() sc.nextInt sc int c = sc.nextInt(); c sc.nextInt() sc.nextInt sc int d = sc.nextInt(); d sc.nextInt() sc.nextInt sc long max = (long)b*d; max (long)b*d (long)b d long[] cross = {(long)b*d,(long)a*c,(long)a*d,(long)b*c}; cross {(long)b*d,(long)a*c,(long)a*d,(long)b*c} (long)b*d (long)b d (long)a*c (long)a c (long)a*d (long)a d (long)b*c (long)b c for(int i=0; i<cross.length; i++){
      if(max<cross[i]){
        max = cross[i];
      }
    } int i=0; int i=0; i 0 i<cross.length i cross.length cross cross.length i++ i++ i {
      if(max<cross[i]){
        max = cross[i];
      }
    } {
      if(max<cross[i]){
        max = cross[i];
      }
    } if(max<cross[i]){
        max = cross[i];
      } max<cross[i] max cross[i] cross i {
        max = cross[i];
      } max = cross[i] max cross[i] cross i System.out.println(max) System.out.println System.out System System.out max String[] args args 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);

	}
} 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);

	}
} Main
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);

	}
}
