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: Wrong Answer)

#include<stdio.h>

int main(void){

    int N,i,j,R_num = 0,G_num = 0,B_num = 0;
    long int ans;
    char S[4001];

    scanf("%d",&N);
    scanf("%s",S);
    
    for(i = 0;i < N;i++){
        if(S[i] == 'R') R_num++;
        else if(S[i] == 'G') G_num++;
        else if(S[i] == 'B') B_num++;
    }

    ans = R_num * G_num * B_num;

    for(i = 0;i < N;i++){
        for(j = 1;(i+j+j) < N;j++){
            if(S[i] != S[i+j] && S[i+j] != S[i+j+j] && S[i+j+j] != S[i]) ans--;
        }
    }

    printf("%ld\n",ans);
    return 0;
}