D. AB-stringtime limit per test2 secondsmemory limit per test256 megabytesinputstandard inputoutputstandard outputThe string t_1t_2 \dots t_k is good if each letter of this string belongs to at least one palindrome of length greater than 1.A palindrome is a string that reads the same backward as forward. For example, the strings A, BAB, ABBA, BAABBBAAB are palindromes, but the strings AB, ABBBAA, BBBA are not.Here are some examples of good strings:   t = AABBB (letters t_1, t_2 belong to palindrome t_1 \dots t_2 and letters t_3, t_4, t_5 belong to palindrome t_3 \dots t_5);  t = ABAA (letters t_1, t_2, t_3 belong to palindrome t_1 \dots t_3 and letter t_4 belongs to palindrome t_3 \dots t_4);  t = AAAAA (all letters belong to palindrome t_1 \dots t_5); You are given a string s of length n, consisting of only letters A and B.You have to calculate the number of good substrings of string s.InputThe first line contains one integer n (1 \le n \le 3 \cdot 10^5) — the length of the string s.The second line contains the string s, consisting of letters A and B.OutputPrint one integer — the number of good substrings of string s.ExamplesInput
5
AABBB
Output
6
Input
3
AAA
Output
3
Input
7
AAABABB
Output
15
NoteIn the first test case there are six good substrings: s_1 \dots s_2, s_1 \dots s_4, s_1 \dots s_5, s_3 \dots s_4, s_3 \dots s_5 and s_4 \dots s_5.In the second test case there are three good substrings: s_1 \dots s_2, s_1 \dots s_3 and s_2 \dots s_3.
5
AABBB

6 
['binary search', 'combinatorics', 'dp', 'strings', '*1900']