Period of Words

A string is a finite sequence of lower-case (non-capital) letters of the
English alphabet. Particularly, it may be an empty sequence, i.e. a
sequence of 0 letters. By A = BC we denotes that A is a string obtained by
concatenation (joining by writing one immediately after another, i.e.
without any space, etc.) of the strings B and C (in this order). A string P
is a prefix of the string A, if there is a string B, that A = PB. In other
words, prefixes of A are the initial fragments of A. In addition, if P != A
and P is not an empty string, we say, that P is a proper prefix of A. 
A string Q is a period of A, if Q is a proper prefix of A and A is a prefix
(not necessarily a proper one) of the string QQ. For example, the strings
abab and ababab are both periods of the string abababa. The maximum period
of a string A is the longest of its periods or the empty string, if A
doesn't have any period. For example, the maximum period of ababab is abab.
The maximum period of abc is the empty string. 
Task:

Write a programme that: 
 * reads in the string's length and the string itself, 
 * calculates the sum of lengths of maximum periods of all its prefixes, 
 * writed out the result

PROBLEM NAME: okr  (this is another problem whose acronym is in Polish!)

INPUT FORMAT:

In the first line of the standard input there is one integer k ( 1 <=
k <= 1 000 000) -- the length of the string. In the following line a
sequence of exactly k lower-case letters of the English alphabet is
written -- the string.

SAMPLE INPUT:

8
babababa

OUTPUT FORMAT:

In the first and only line of the standard output your programme
should write an integer -- the sum of lengths of maximum periods of
all prefixes of the string given in the input.

SAMPLE OUTPUT:

24