OBM 2008 Problem 6

The venusian prophet Zabruberson sent to his pupils a $10000$ -letter word, each letter being $A$ or $E$ : the Zabrubic word. Their pupils consider then that for $1 \leq k \leq 10000$ , each word comprised of $k$ consecutive letters of the Zabrubic word is a prophetic word of length $k$ . It is known that there are at most $7$ prophetic words of lenght $3$ . Find the maximum number of prophetic words of length $10$ .