program p1;
var a:array[0..4] of integer;
    f,g:text;
    i,j,aux:integer;
begin
for i:=1 to 4 do read(a[i]);
for i:=1 to 3 do
        for j:=i+1 to 4 do
                if a[i]<a[j] then begin
                                aux:=a[i];
                                a[i]:=a[j];
                                a[j]:=aux;
                                        end;
writeln(a[1]*a[2]+a[3]*a[4]);

end.