program ex;
var
cx,co,mx,mo,minm,minc:longint;

begin
  assign(input,'bs.in');
  assign(output,'bs.out');
  reset(input);
  rewrite(output);
  while not eof(input) do
  begin
    readln(co,cx,mo,mx);
    if (co=0) or (mo=0) then
      if (cx=0) or (mx=0) then writeln('0') else if (cx<mx) then writeln(cx) else writeln(mx)
      else
      if (cx=0) or (mx=0) then
      if (co=0) or (mo=0) then writeln('0') else if (co<mo) then writeln(co) else writeln(mo)
      else
      if ((cx*mo+mo)>co)and((co*mx+mx)>cx) then writeln(co+cx)
      else
      begin
        if (cx<co) then minc:=cx else minc:=co;
        if (mx<mo) then minm:=mx else minm:=mo;
        writeln(minm*minc+minm+minc);
      end;
  end;
  close(input);
  close(output);
end.