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++ (Clang 10.0.0) (judge verdict: Wrong Answer)

#include <iostream>
#include<stdio.h>
using namespace std;
int main()
{
    int n,ans=0;
    scanf("%d",&n);
    char a[n];
    for(int i=0;i<n;i++)
    {
        scanf("%c",&a[i]);
    }
    for(int i=0;i<n-2;i++)
        for(int j=i+1;j<n-1;j++)
        for(int k=j+1;k<n;k++)
    {
        if(a[i]!=a[j]&&a[i]!=a[k]&&a[j]!=a[k]&&2*j!=i+k)
        {
            ans++;
        }
    }
    cout<<ans;
    return 0;
}