Tommy likes the RGB keyboard. He would like to see how many RGB-words are in a given string ~s~. An RGB-word is defined as a substring that starts with an R and ends with a B, and between this R and the B letter G appears exactly once. For example, RGB, and RAGB are RGB-words. However, RGGB is not an RGB-word. You are given a string ~s~, Tommy would like to know how many RGB-words are there in the string, can you write a program to help him?

Input Specification

The first line contains an integer ~N~, denoting the length of the given string ~s~.

The second line contains the given string ~s~, consisting of only capital English letters.

The following table shows how the available ~15~ marks are distributed.

Marks Awarded	~N~
~3~ marks	~1 \leq N \leq 500~
~3~ marks	~1 \leq N \leq 5000~
~9~ marks	~1 \leq N \leq 10^6~

Output Specification

The first and only line of output contains a single integer, representing the number of RGB-words found in the given string ~s~.

Sample Input 1

4
RBGB

Sample Output 1

1

Explanation for Sample 1

RBGB is the only RGB-word that occurs in this case. Note that RB is not an RGB-word.

Sample Input 2

5
RGBAB

Sample Output 2

2

Explanation for Sample 2

RGB and RGBAB are RGB-words. Thus, there are a total of ~2~ RGB-words in the given string ~s~.

Sample Input 3

4
RGGB

Sample Output 3

0