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>

#define SIZE 4500

int main(){
    int N;
    char S[SIZE] = {};
    scanf("%d%s", &N, S);
    int r, g, b;
    r = g = b = 0;
    for(int i=0; i<N; i++){
        switch(S[i]){
            case 'R': r++; break;
            case 'G': g++; break;
            case 'B': b++; break;
        }
    }
    long long ans = r*g*b;
    
    int i, p;
    for(i=0; i<N-2; i++){
        for(p=1; i+p+p<N; p++){
            if(S[i]!=S[i+p] && S[i]!=S[i+p+p] && S[i+p]!=S[i+p+p]){
                ans--;
            }
        }
    }

    printf("%lld\n", ans);
}