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<bits/stdc++.h>
using namespace std;

int main(){
	int l;
	char s[4010];
	long long sum=0;
	
	scanf("%d",&l);
	scanf("%s",s);
	
	for(int i=0;i<l-2;i++){
		for(int j=i+1;j<l-1;j++){
			for(int k=j+1;k<l;k++){
				if(s[i]!=s[j]&&s[i]!=s[k]&&s[j]!=s[k]&&(j-i!=k-j)){
					sum++;
				}
			}
		}
	}
	printf("%lld\n",sum);
	
	return 0;
}