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<string.h>
#include <stdlib.h>
int main(void){
    int N;
    char S[4001];
    scanf("%d",&N);
    scanf("%s",S);
    int SUM=0;
    for (int i=0; i<N-2; i++) {
        for (int j=i+1; j<N-1; j++) {
            for (int l=j+1; l<N; l++) {
                if (S[i]!=S[j] && S[i]!=S[l] && S[j]!=S[l]) {
                    if (j-i!=l-j) {
                        SUM++;
                    }
                }
            }
        }
    }
    printf("%d\n",SUM);
    return 0;
}