var stri: string; arr: array['A'..'z'] of byte; i: char; z: byte;
begin
write('Nhap chuoi dem: ');
readln(stri);
for i:='A' to 'z' do arr[i]:=0;
for z:=1 to length(stri) do inc(arr[stri[z]]);
for i:='A' to 'z' do
if (arr[i]>=2) then write(i,' ');
readln
end.