function switchTop20 (flag) {
 for (var i=6;i<=20;i++) {

  if (flag) {
   SwapNav('top'+i,'show')
  } else {
   SwapNav('top'+i,'hide')  
  }
 }
  
 /*прячем навигац. строку*/

 if (flag) {
  SwapNav('top20hide','show')
  SwapNav('top20show','hide')

 } else {
  SwapNav('top20hide','hide') 
  SwapNav('top20show','show')
 }

}