how to build a installer which installed in program files in both 64 and 32 bit machines

[Setup]
DefaultDirName={code:GetProgramFiles}\{#MyAppName}

[code]
function GetProgramFiles(Param: string): string;
begin
  if IsWin64 then Result := ExpandConstant('{pf64}')
    else Result := ExpandConstant('{pf32}')
end;