#include <bits/stdc++.h>

using namespace std;
#define int long long
 #define mod 1000000007
 #define mx 20000
 
int spf[mx];
int val[mx];
void sieve()
{
    spf[1]=1;
    for(int i=3;i<mx;i+=2)
    {
        spf[i]=i;
    }
    for(int i=2;i<mx;i+=2)
    {
        spf[i]=2;
    }
    for(int i=3;i<mx;i++)
    {
        if(spf[i]==i)
        {
            for(int j=i*i;j<mx;j+=i)
            {
                if(spf[j]==j)
                {
                    spf[j]=i;
                }
            }
        }
    }
    
    val[1]=0;
    for(int i=2;i<mx;i++)
    {
     if(spf[i/spf[i]]!=spf[i])
     {
         val[i]=1+val[i/spf[i]];
     }
     else
     {
         val[i]=val[i/spf[i]];
     }
    }
}
 
 vector<vector<int>>g;
 
int n,k;
vector<int>sz;
int ans;

long long binpow(long long a, long long b) {
    if (b == 0)
        return 1;
    long long res = binpow(a, b / 2);
    if (b % 2)
        return (( (res * a)%mod) * res)%mod;
    else
        return (res * res)%mod;
}
 
 int inv(int p)
 {
     return (binpow(p,mod-2));
 }
 
 void dfs(int node,int p)
 {
     sz[node]=1;
     for(auto i:g[node])
     {
         if(i!=p)
         {
             dfs(i,node);
             sz[node]=(sz[node]+sz[i]);
         }
     }
    
    
     
 }
 
 int dfs1(int node,int p)
 {
     
     int ans=0,c=0;
     int u=0,v=0;
    for(auto i:g[node])
     {
         if(i!=p)
         {
             c++;
             if(c==1)
             {
                 u=i;
             }
             if(c==2)
             {
                 v=i;
             }
         }
     }
     if(c==0)
     {
         return 0;
     }
     if(c==1)
     {
         return sz[u]-1;
     }
    
     return max( sz[u]-1+dfs1(v,node),sz[v]-1+dfs1(u,node));
 }

 int lcm(int x,int y)
 {
     int temp= x*y;
     temp/=(__gcd(x,y));
     return temp;
 }
 
int reverseDigits(int num) {
    int rev_num = 0;
    while (num > 0) {
        rev_num = rev_num * 10 + num % 10;
        num = num / 10;
    }
    return rev_num;
}
 
bool isP(int n) {
    int rev_n = reverseDigits(n);
    return (rev_n == n);
}
 
void solve()
{
int a[4];
for(int i=0;i<4;i++)
{
    cin>>a[i];
}
sort(a,a+4);
cout<<a[0]*a[2]<<endl;



}
 
signed main()
{
    
    // sieve();

    int t=1;

    while(t--)
    {
        solve();
    }
 
    return 0;
}