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)

#include<stdio.h>
#include<stdlib.h>
int main()
{
	char a[4010];
	int i, j, k,n;
	long long int num = 0;
	scanf("%d%s", &n, a);
	for (i = 0; i < n-2; i++)
	{
		for (j = i + 1; j < n-1; j++)
		{
			for (k = j + 1; k < n; k++)
			{
				if (a[i] != a[j] && a[i] != a[k] && a[j] != a[k] && i + k != j + j)
				{
					num++;
				}
			}
		}
	}
	printf("%lld", num);
	return 0;
}