Where is the mistake in my program?
I got WA on test 7

var litere:string;
    afis,s,x:array[1..260000]of char;
    i,j,k,nr,af:longint;
begin
  for i:=65 to 90 do litere:=litere+chr(i);
  for i:=97 to 122 do litere:=litere+chr(i);
  while not eof do begin
    inc(nr);
    read(s[nr]);
  end;
  i:=1;
  while i<nr do begin
    while (pos(s[i],litere)=0)and(i<=nr) do begin inc(af);afis[af]:=s[i];inc(i);end;
    j:=i;
    while (pos(s[i],litere)<>0)and(i<=nr) do inc(i);
    for k:=i-1 downto j do begin
      inc(af);
      afis[af]:=s[k];
    end;
  end;
  for i:=1 to af do write(afis[i]);
end.