Problem:
Score : 400 points

Problem Statement

We have a string S of length N consisting of R, G, and B.

Find the number of triples (i,~j,~k)~(1 \leq i < j < k \leq N) that satisfy both of the following conditions:

S_i \neq S_j, S_i \neq S_k, and S_j \neq S_k.

j - i \neq k - j.

Constraints

1 \leq N \leq 4000

S is a string of length N consisting of R, G, and B.

Input

Input is given from Standard Input in the following format:

N
S

Output

Print the number of triplets in question.

Sample Input 1

4
RRGB

Sample Output 1

1

Only the triplet (1,~3,~4) satisfies both conditions. The triplet (2,~3,~4) satisfies the first condition but not the second, so it does not count.

Sample Input 2

39
RBRBGRBGGBBRRGBBRRRBGGBRBGBRBGBRBBBGBBB

Sample Output 2

1800

Solution in C++ (GCC 9.2.1) (judge verdict: Time Limit Exceeded)

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;
int main()
{
	int a;
	int cnt = 0;
	string in;
	cin >> a;
	cin >> in;
	for (int i = 0; i < a; i++) {
		char t1 = in[i];
		for (int j = i + 1; j < a; j++) {
			char t2 = in[j];
			if (t1 == t2) continue;
			for (int k = j + 1; k < a; k++) {
				char t3 = in[k];
				if (k - j == j - i) continue;
				if (t3 == t1 || t3 == t2) continue;
				cnt++;
			}
		}
	}
	cout << cnt << endl;



}