Tìm xem có bao nhiêu chữ O:
c c c c c c c c c c c c c c c c c c c c c c c c o c c c c c c c c c c c c c c c c c c c
c c c o c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c o c c
c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c o c c c c c c c c c c c c c
c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c
c c c c c c c c c c c c c c c c c c c o c c c c c c c c c c c c c c c c c c c c c c c
có 5 chữ o
5 chữ o