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)

int main(){
    int N,count=0;
    scanf("%d",&N);
    char *s=(char*)malloc(sizeof(char)*(N+1));
    scanf("%s",s);

    for(int i=1;i<=N-2;i++){
        for(int j=i+1;j<=N-1;j++){
            for(int k=j+1;k<=N;k++){
                if(s[i-1]!=s[j-1] && s[j-1]!=s[k-1] && s[i-1]!=s[k-1] && j-i!=k-j){
                    count++;
                }
            }
        }
    }

    printf("%d\n",count);
    return 0;

}