var v:array[1..100]of integer;
    n,i,j,aux:integer;


begin
     n:=4;

     for i:=1 to n do
     read(v[i]);


     for i:=1 to n-1 do
     for j:=i+1 to n do
     begin
     If v[i]<v[j] then
     begin
     aux:=v[i];
     v[i]:=v[j];
     v[j]:=aux;
     end;
     end;


     write(v[1]*v[2]+v[3]*v[4]);

     readln;
     readln;
     end.