/*
 ______   _________ _      _       _
|  ____ \|___   ___| |    | |     | |
| |    \ \   | |   | |____| |     | |
| |    | |   | |   |  ____  |     | |
| |____/ /___| |___| |    | |_____| |
|_______/|_________|_|    |_________|

*/
#define INF 1e18 
#define fi first 
#define sz size()
#define se second 
#define sll set<ll>
#define two(n) 1<<n
#define eif else if
#define ms multiset
#define mm multimap
using namespace std;
#define len length()
#define ll long long
#define pb push_back
#define mt make_tuple
#define pf push_front
#define mll map<ll,ll>
#define MOD 1000000007
#define vll vector<ll>
#define ___ cout<<endl
#define popb pop_back()
#define ss stringstream
#define popf pop_front()
#include <bits/stdc++.h>
#define rf(i,a,n) for(i=a;i>n;i--) 
#define rptr(x) x.rbegin(),x.rend()
#define min3(a,b,c) min(min(b,c),a)
#define minof(x) min_element(ptr(x))
#define hex_out(a) cout<<hex<<a<<endl 
#define out2(a,b) cout<<a<<" "<<b<<endl
#define yn(a) cout<<(a>0?"YES":"NO")<<endl
#define dir_4 vll dx{1,0,-1,0},dy{0,1,0,-1}
#define bool_out(a) cout<<boolalpha<<a<<endl
#define char_out(x) printf("%c",x);cout<<endl
#define scien_out(a) cout<<scientific<<a<<endl
#define v_in(x,n) vll x(n);for(auto &i:x) cin>>i
#define rpqll priority_queue<ll,vll,greater<int>>
#define ub(x,a) upper_bound(x.begin(),x.end(),a)-x.begin()
#define vp_in(x,n) vpll x(n); for(auto &i:x)cin>>i.fi>>i.se
#define precision(n,a) cout<<fixed<<setprecision(a)<<n<<endl
#define dir_8 vll dx{1,1,0,-1,-1,-1,0,1},dy{0,1,1,1,0,-1,-1,-1}
#define dir_horse vll dx{2,1,-1,-2,-2,-1,1,2},dy{1,2,2,1,-1,-2,-2,-1}
#define month(y) ll month[]={-1,31,leapyear(y)?29:28,31,30,31,30,31,31,30,31,30,31}
#define v2_in(x,n,m) vector<vector<int>> x(n,vector<int>(m)); f(i,0,n)for(auto &j:x[i]) cin>>j
#define m_in(x,n) mll x; for(i=0,int a,b;i<n, cin>>a>>b;i++) x[a]=b
#define s_in(x,n) sll x;for(ll a,i=0;i<n;cin>>a,i++)x.insert(a)
#define v_in2(x,y,n) vll x(n),y(n); f(i,0,n) cin>>x[i]>>y[i]
#define lb(x,a) lower_bound(x.begin(),x.end(),a)-x.begin()
#define inrange(i,a,b) ((i>=min(a,b))&(i<=max(a,b)))
#define out3(a,b,c) cout<<a<<" "<<b<<" "<<c<<endl
#define maxof(x) max_element(x.begin(),x.end())
#define revers(x) reverse(x.begin(),x.end()) 
#define delete(x,a) x.erase(find(ptr(x),a)) 
#define bs(x,a) binary_search(ptr(x),a) 
#define max3(a,b,c) max(max(b,c),a) 
#define f(i,a,n) for(i=a;i<n;i++)
#define ptr(x) x.begin(),x.end() 
#define ull unsigned long long 
#define lcm(a,b) a*b/gcd(a,b)
#define tll tuple<ll,ll,ll> 
#define tup(x,i) get<i>(x) 
#define b_s binary_search 
#define vs vector<string>
#define um unordered_map
#define vull vector<ull>
#define u_b upper_bound 
#define l_b lower_bound 
#define vb vector<bool> 
#define vc vector<char> 
#define pll pair<ll,ll> 
#define vpll vector<pll> 
#define us unordered_set 
#define clr(x) x.clear() 
#define vtll vector<tll> 
#define pq priority_queue 
#define mcll map<char,ll>
#define max_of max_element
#define min_of min_element
#define msll map<string,ll>
#define vvll vector<vector<ll>>
#define vvc vector<vector<char>>
#define str_in(x) string x; cin>>x
#define digit(n) floor(log(n)/2.0)+1
#define srt(x) sort(x.begin(),x.end())
#define _fill(x,a) memset(x,a,sizeof(a)) 
#define rsrt(x) sort(x.rbegin(),x.rend())
#define pi 3.141592653589793238462643383279
#define rotate_l(x,a) rotate(x.bg,x.bg+a,x.ed)
#define vs_in(x,n) vs x(n);for(auto &i:x) cin>>i 
#define rotate_r(x,a) rotate(x.bg,x.bg+x.sz-a,x.ed)
#define ____ ios::sync_with_stdio(0);cin.tie(nullptr);
ll d_sum(ll n){ll s=0;while(n>0)s+=n%10,n/=10;return s;}
template<typename T>T pstv(T x){if(x<0)return 0;return x;}
ll rev(ll n){ll a=0; while(n) {a=a*10+n%10;n/=10;} return a;}
void vs_out(vector<string> x) {for(auto i:x) cout<<i<<endl;}
template<typename T>T ngtv(T x){if(x<0)return 0; else return x;} 
bool leapyear(ll n){if(n%400==0|(n%4==0&n%100>0))return 1;return 0;}
template<typename T1,typename T2>T1 max(T1 a,T2 b){return (b>a)?b:a;}
template<typename T1,typename T2>T1 min(T1 a,T2 b) {return (b<a)? b:a;}
void tolwr(string &x){ll i,n=x.size();for(i=0;i<n;i++) x[i]=tolower(x[i]);}
void toupr(string &x){ll i,n=x.size(); for(i=0;i<n;i++) x[i]=toupper(x[i]);}
template<typename T>ull fact(T n){ull i,c=1;for(i=2;i<n+1;i++)c*=i;return c;} 
template<typename T>ll sum(vector<T> x) {ll s=0; for(auto i:x) s+=i; return s;} 
bool issubstr(string x, string y){if(x.find(y)!=string::npos)return 1;return 0;}
template<typename T1,typename T2>void swap(T1 *a,T2 *b) {*a^=*b; *b^=*a; *a^=*b;}
template<typename T>void v_out(vector<T> x){for(auto i:x)cout<<i<<" "; cout<<endl;}
bool compare(int a,int b){/* return a<b;//ascending */ return a>b; /* //descending*/}
ll divisor(ll n){ll i,c=0; for(i=1;i*i<n;i++) if(n%i==0) c+=2; if(i*i==n)c++;return c;}
//tree//void dfs(ll prev,ll current){for(auto i:adj[current])if(i!=prev)dfs(current,i);}
template<typename T>ull lcmof(vector<T> x){T s=x[0]; for(auto i:x) s=lcm(s,i); return s;} 
template<typename T>void pre_sum(vector<T>x) { ll i,n=x.size(); for(i=1;i<n;i++)x[i]+=x[i-1];}
template<typename T> void adjdif(vector<T>&x){ll n=x.size(),i;for(i=n-1;i>-1;i++) x[i]-=x[i-1];}
//graph//void dfs(ll node){if(visited[node])return;visited[node]=1;for(auto i:adj[node]) dfs(i);}
template<typename T1,typename T2>ull npr(T1 n,T2 r){ull s=1,i;for(i=n-r+1;i<n+1;i++)s*=i;return s;}
template<typename T1,typename T2>void m_out(map<T1,T2>x){for(auto i:x) cout<<i.fi<<" "<<i.se<<endl;}
template<typename T>ull gcdof(vector<T> x){T s=0;for(auto i:x) {s=gcd(s,i); if(s==1)break;} return s;}
void LPS(string pat,ll m, vll &lps){for(ll i=1,j=0;i<m;i++)pat[j]==pat[i]?lps[i++]=++j:j?j=lps[j-1]:i++;}
bool vowel(char c){c=tolower(c);if((c=='a')|(c=='e')|(c=='i')|(c=='o')|(c=='u')) return 1; else return 0;}
bool palindrome(string x){ll n=x.size(),i; for(i=0;i<ceil(n/2.0);i++) if(x[i]!=x[n-i-1]) return 0; return 1;}
void out(){cout<<endl;}template <typename T1, typename... T2>void out(T1 a, T2 ... b){cout<<a<<" ";out(b ...);} 
template<typename T1,typename T2>ull _pow(T1 x,T2 n){ull s=1,a=x;while(n>0){if(n%2==1)s*=a;a*=a;n/=2;}return s;}
void substr(string x){ll n=x.sz,i,j,k; for(i=0;i<n;i++) for(j=i+1;j<n+1;j++) {for(k=i;k<j;k++) cout<<x[k]; cout<<endl;}}
template<typename T1,typename T2>ull ncr(T1 n,T2 r){ull s=1,i; if(r>n-r)r=n-r;for(i=1;i<r+1;i++)s=(s*(n-r+i))/i; return s;}
void strseq(string x,string y,ll i){if(i==x.size()){if(y.size()>0) out(y);}else{strseq(x,y,i+1);y+=x[i]; strseq(x,y,i+1);}}
string spell(ll n){vector<string> num={" ","one","two","three","four","five","six","seven","eight","nine"}; return num[n];}
template<typename T>void v2_out(vector<vector<T>> x) {T i,n=x.sz; for(i=0;i<n;i++) { for(auto j:x[i]) cout<<j<<" "; cout<<endl;}}
template<typename T>void subarr(vector<T> x){ll n=x.sz,i,j,k;for(i=0;i<n;i++)for(j=i+1;j<n+1;j++){for(k=i;k<j;k++)cout<<x[k]<<" ";cout<<endl;}}
bool prime(ll n){if(n<=1)return 0;if(n<=3)return 1;if(n%2==0|n%3==0)return 0;for(ll i=5;i*i<=n;i=i+6)if((n%i==0)|(n%(i+2)==0))return 0;return 1;}  
template<typename T>void arrseq(vector<T> x,vector<T> y,ll i) {if(i==x.size()) if(y.size()>0) v_out(y); else{arrseq(x,y,i+1); y.pb(x[i]); arrseq(x,y,i+1);}}
int lps(string seq,ll i,ll j){if(i==j) return 1;if(seq[i]==seq[j]&i+1==j)return 2;if(seq[i]==seq[j])return lps(seq,i+1,j-1)+2;return max(lps(seq,i,j-1),lps(seq,i+1,j));} 
//void bfs(ll a){queue<ll> q;dist[a]=0;q.push(a);while(!q.empty()){ll u=q.front(),v;q.pop();for(auto i:adj[u]){v=i;if(dist[v]==INT_MAX){dist[v]=dist[u]+1; q.push(v);}}}}
ll kmp(string txt,string pat) {ll m=pat.size(),n=txt.size();vll lps(m);LPS(pat,m,lps);for(ll i=0,j=0;i<n;){pat[j]==txt[i]?i++,++j:j?j=lps[j-1]:i++;if(j==m){return i-j+1;}}return -1;}
ll minpathsum(vvll x,ll n,ll m){vvll dp(n,vll(m));ll i,j;for(i=0;i<n;i++)for(j=0;j<n;j++)dp[i][j]=x[i][j]+min(i>0?dp[i-1][j]:j==0?0:INF,j>0?dp[i][j-1]:i==0?0:INF);return dp[n-1][m-1];}
bool anagram(string x,string y){map<char,ll> c;ll i,n=x.length(),m=y.length(),s=0;if(n!=m)return 0;for(i=0;i<n;i++){ll a=x[i],b=y[i];if(c[a]<0)s++;c[a]++;if(c[b]>0)s++;c[b]--;}if(s==n)return 1;return 0;}
template<typename T1,typename T2>ull gcd(T1 a,T2 b) {if(a==0|b==0)return a|b;unsigned shift=__builtin_ctz(a|b);a>>=__builtin_ctz(a);do{b>>=__builtin_ctz(b);if(a>b)swap(&a,&b);b-=a;}while(b>0);return a<<shift;}
#define MAX 100001
ll t,n,i,j,k,a,b,c,d,m,l,r,p,q,s,ans;
void dihan()
{
	cin>>a>>b>>c>>d;

	cout<<max(max(b*d,a*c),max(a*d,b*c));
}
int main(){____ dihan();}

Measured memory_bytes: 3660