#include <cstdio>
#include <algorithm>
#define pb push_back
#define mp make_pair
#define ld long double
#define ll long long
#define ull unsigned long long
using namespace std;
#define f cin
#define g cout

//ifstream f(".in");
//ofstream g(".out");

int main()
{
     int v[10],sol=0;
     for(int i=1;i<=4;++i)scanf("%d",&v[i]);
     sort(v+1,v+1+4);
     do
     {
          sol=max(sol,v[1]*v[2]+v[3]*v[4]);
     }while(next_permutation(v+1,v+1+4));
     printf("%d\n",sol);
     //f.close();g.close();
     return 0;
}