Const
 Delimiters =
   ['/', '?', '.', ',', '<', ';', '>',
    ':', '"', '!', '''', '*', '%'];


Const
 s: String = 'stststsrtsrtsee>>!%rstrstrstrtkk%<<opopopop??';
 n = 2;
 substr: String = 'st';


Function GetFirstWord(s: String;
        Var Start, Finish: Byte): String;
 Begin
   Start := 1;
   While s[Start] In Delimiters Do
     Inc(Start);
   Finish := Start;
   While not (s[Finish] In Delimiters) Do
     Inc(Finish);

   GetFirstWord := Copy(s, Start, Finish - Start)
 End;

Function CountSubs(s, subs: String): Byte;
 Var
   p, count: Byte;
 Begin
   Count := 0;
   Repeat
     p := Pos(subs, s);
     If p <> 0 Then
       Begin
         Delete(s, p, Length(subs));
         Inc(count)
       End
   Until p = 0;
   CountSubs := count
 End;

Var
 iPos, wStart, wFinish: Byte;
 WordsDeleted: Byte;
 FirstWord: String;
begin
 iPos := 1; WordsDeleted := 0;
 Repeat
   FirstWord := GetFirstWord(Copy(s, iPos, Length(s)), wStart, wFinish);

   If FirstWord <> '' Then
     Begin
       If CountSubs(FirstWord, substr) = 3 Then
         Begin
           Delete(s, wStart, wFinish - wStart);
           Inc(WordsDeleted)
         End
       Else Inc(iPos, Pred(wFinish));

       If WordsDeleted = n Then Break
     End

 Until FirstWord = '';

 Writeln('Result string: ', s)
End.