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<bits/stdc++.h>
using namespace std;
#define ll long long int 
#define f first
#define s second
#define pb push_back
#define mod 1000000007
#define mp make_pair
#define fast 
#define f first
#define s second
#define endl "\n"
#define pie 3.1415926535

int main(){
    int n;
    cin >>n;
    string s;
    cin >> s;
  
    long long sum = 0;
    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(s[i] != s[j] && s[j]!= s[k] && s[i]!=s[k] && (j-i)!=(k-j))
                    sum++;
            }
        }
    }
    cout << sum<<endl;
    return 0;
    
}