#include <cmath>
#include <climits>
#include <queue>
#include <vector>
#include <map>
#include <set>
#include <cstdlib>
#include <fstream>
#include <iomanip>   
#include <iostream>  
#include <sstream>  // istringstream buffer(myString);
#include <stack>
#include <algorithm>
#include <cstring>
#include <bitset>
#include <cassert>
#include<bits/stdc++.h>

using namespace std;
#define bit(x,i) (x&(1<<i))  //select the bit of position i of x
#define lowbit(x) ((x)&((x)^((x)-1))) //get the lowest bit of x
#define hBit(msb,n) asm("bsrl %1,%0" : "=r"(msb) : "r"(n)) //get the highest bit of x, maybe the fastest
#define max(a,b) (a<b?b:a)
#define pwrtwo(x) (1 << (x))
//#define abs(x) (x<0?(-x):x) // big bug here if "-x" is not surrounded by "()"
#define IN(i,l,r) (l<i&&i<r) //the next for are for checking bound
#define ll long long //data types used often, but you don't want to type them time by time
#define ull unsigned long long
#define ui unsigned int
#define us unsigned short
#define IOS ios_base::sync_with_stdio(0); //to synchronize the input of cin and scanf
#define INF 1001001001
#define PI 3.1415926535897932384626
#define LINR(i,l,r) (l<=i&&i<=r)
#define LIN(i,l,r) (l<=i&&i<r)
#define INR(i,l,r) (l<i&&i<=r)
#define F(i,L,R) for (int i = L; i < R; i++) //next four are for "for loops"
#define FE(i,L,R) for (int i = L; i <= R; i++)
#define FF(i,L,R) for (int i = L; i > R; i--)
#define FFE(i,L,R) for (int i = L; i >= R; i--)
#define getI(a) cin>>a //next three are handy ways to get ints, it's also force you to use '&' sign
#define getII(a,b) cin>>a>>b
#define getIII(a,b,c) cin>>a>>b>>c
#define sc(n) ll (n); cin>>n //handy if the input is right after the definition of a variable
#define sc2(n,m) ll (n),(m); cin>>n>>m
#define sc3(n,m,k) ll (n),(m),(k); cin>>n>>m>>k
#define scarr(arr,n) ll arr[n]; for(int i=0;i<n;i++)getI(arr[i]);
#define scarrn(arr,n) ll arr[n+1]; for(int i=1;i<=n;i++)getI(arr[i]);
#define TESTS sc(testow);while(testow--) //for multilple cases problems
#define whileZ int T; getI(T); while(T--) // the same as above
#define getS(x) scanf("%s", x) //get a char* string
#define clr(a,x) memset(a,x,sizeof(a)) //set elements of array to some value
#define char2Int(c) (c-'0')
#define lastEle(vec) vec[vec.size()-1] 
#define SZ(x) ((int)((x).size()))
#define REMAX(a,b) (a)=max((a),(b)) // set a to the maximum of a and b
#define REMIN(a,b) (a)=min((a),(b));
#define FOREACH(i,t) for (typeof(t.begin()) i=t.begin(); i!=t.end(); i++) // traverse an STL data structure
#define ALL(c) (c).begin(),(c).end() //handy for function like "sort()"
#define PRESENT(c,x) ((c).find(x) != (c).end()) 
#define CPRESENT(c,x) (find(ALL(c),x) != (c).end()) 

/// cout 
//#define c_ cout
//for map, pair
#define mp make_pair
#define fi first
#define se second
// for debug
inline void pisz(int n) { printf("%d\n",n); }
#define DBG(vari) cerr<<#vari<<" = "<<(vari)<<endl;
#define printA(a,L,R) FE(i,L,R) cout << a[i] << (i==R?'\n':' ')
#define printV(a) printA(a,0,a.size()-1)
#define MAXN 10000
#define c_sum(a,b,n) F(i,0,n)if(i==0)b[i]=a[i];else b[i]=b[i-1]+a[i] 
//for vectors
#define pb push_back
typedef int elem_t;
typedef vector<int> vi; 
typedef vector<vi> vvi; 
typedef pair<int,int> ii; 
// directions
const int fx[4][2] = {{0,1}, {0,-1}, {1,0}, {-1,0}};
const int fxx[8][2] = {{0,1}, {0,-1}, {1,0}, {-1,0}, {1,1}, {1,-1}, {-1,1}, {-1,-1}};
template<typename T,typename TT> ostream& operator<<(ostream &s,pair<T,TT> t) {return s<<"("<<t.first<<","<<t.second<<")";}
template<typename T> ostream& operator<<(ostream &s,vector<T> t){F(i,0,SZ(t))s<<t[i]<<" ";return s; }
 
 
// bbbacdaddb


 
int main(int argc, char const *argv[])
{
	// cout<<"hiuh";
    #ifndef ONLINE_JUDGE  
    freopen("input.txt", "r", stdin); 
    freopen("output.txt", "w", stdout);   
    #endif 
    ios_base::sync_with_stdio(false);
 
    
    long long a,b,c,d;
    cin>>a>>b>>c>>d;

    cout<<max( a*c, max( b*d, max( a*d, b*c )) );

    return 0;
}

Measured memory_bytes: 3644