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>
int main()
{
  int N;
  scanf("%d",&N);
  char A[N+1];
  int i;
  for(i=0;i<N+1;i++){
    scanf("%c",&A[i]);
  }
  int j,k;
  int sum=0;
  for(i=1;i<N-1;i++){
    for(j=i+1;j<N;j++){
      for(k=j+1;k<N+1;k++){
        if(((A[i]!=A[j])&&(A[j]!=A[k]))&&((A[k]!=A[i])&&(j-i!=k-j))){
            sum++;
          
        }
      }
    }
  }
  printf("%d",sum);
  return 0;
}