program spellchecker;
 var ch:char;
     state:integer;
     errors:integer;
    begin
    state:=0;
    errors:=0;
    while not eof do begin
      read(ch);
      case state of
        0: begin
                         if ch in ['a'..'z']
then inc(errors);
             if ch in ['a'..'z']+['A'..'Z'] then state:=1;
                   end;
        1: begin
             if ch in ['A'..'Z'] then inc(errors);
             if not (ch in ['a'..'z']+['A'..'Z']) then
                  if ch in ['.','!','?'] then state:=0 else state:=2;
           end;
        2: begin
             if ch in ['a'..'z']+['A'..'Z'] then state:=1;
                if ch in ['.','!','?'] then state:=0;
           end;
      end;
    end;
    writeln(errors);
end.

What about this?
"This is a BIG one."
Your program output 2.

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