var x,v,a:array[1..4] of integer;
    i:1..4; max:byte;



 procedure afisare;
 var i:1..4; suma:byte;
 begin

  suma:=v[1]*v[2]+v[3]*v[4];

  if suma>max then begin
                   max:=suma;
                   for i:=1 to 4 do
                       a[i]:=v[i];
                   end;
 end;



 function valid (k:byte):boolean;
 var i:1..4; ok:boolean;
 begin

  i:=1; ok:=true;

  while (i<=k-1) and (ok=true) do
        begin
         if v[i]=v[k] then ok:=false;
         i:=i+1;
        end;

  valid:=ok;
 end;



 procedure bak (k:byte);
 var i:1..4;
 begin

  for i:=1 to 4 do
      begin
       v[k]:=x[i];
       if valid(k) then if k=4 then afisare
          else bak(k+1);
      end;
 end;

begin
 max:=0;

 for i:=1 to 4 do
     read(x[i]);

 bak(1);

 writeln(max);
end.