Description
Small \ (W \) finally learned magic, she can not wait to show you what a small \ (W \) magic is this:
she can be deleted at any one of a string of consecutive sub-string (may be null ), then the rest of the order together into a string.
Small \ (W \) because the just learned magic, she can only be used once.
Small \ (W \) there is a particular favorite string \ (S \) , remaining after you use a magic string is \ (S \) , small \ (W \) will feel their magic satisfied, but not all may make a small string \ (W \) is satisfied.
Small \ (W \) want to know the length \ (n \) string only lowercase letters in, regardless of small \ (W \) how to use the magic will not be satisfied of how many.
Input
A first line integer \ (n-\) , represents the length of the string.
The second row contains only lowercase string \ (S \) .