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 num;
  scanf("%d\n",&num);  
  if(num<3)
    return(0);
  char a[num];
  int ans=0;
  for(int cnt=0;cnt<num;cnt++)
    scanf("%c",&a[cnt]);
    
  for(int i=0;i<num-2;i++)
  {
    for(int j=i+1;j<num-1;j++)
    {
      for(int k=j+1;k<num;k++)
      {
        if(a[i]!=a[j] && a[j]!=a[k] && a[i]!=a[k])
        {
          if(j-i != k-j)
          {
            ans++;
          }
        }
      }
    }
  }
  printf("%d",ans);
}