I don't understand why the answer is find all uncovered position, because in example:

7 2
ioi
1 3

The text that can be formed is:

i o i o i _ _ (with two space in blank or uncovered position)

And the answer if we do that tutorial said, then will be:

26*26=676

But, the string ioioioi is obtained to in that combination, and then the first assumption it's no true, because the string ioi is matched in one more place that input.

thank??