tìm chữ o
00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000o000000000000000000000000000000000000000000000000000000000000000000000000000o0000000000000000000000000000000000000000000000000000000000000000000000000000000000o00000000000000000000000000000000000000000000000o000000000000000000000000000000000000000000000000000000000000000000000