$wc=New-Object System.Net.WebClient
$esc=("\","^","$","(",")","<",".","*","+","?","[","{","|",">")
$url='https://www.master-x.com/forum/forums/22/'
$sbj='Для тех кому за 35-40 (девачкам лучше не читать)'
$tmt=60

$esc|%{$sbj=$sbj.Replace($_,"\$_")}
$sbj=$sbj.Replace(" ","\s")
$ans={[regex]::Match($wc.DownloadString($url),"(?<=($sbj)(.+?\n){6}.+?>)(\d)+(?=(<))").Value}
$old=&$ans

while($true)
{
   $new=&$ans
   if($new -gt $old -and ([System.Windows.Forms.MessageBox]::Show("$($new-$old) штук.`nПометить как прочитанные?","Новые сообщения.",[System.Windows.Forms.MessageBoxButtons]::YesNo)) -eq "Yes")
   {
      $old=$new
   }
   Sleep -Seconds $tmt
}