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: Wrong Answer)

#include <bits/stdc++.h>
using namespace std;
using ll= long long;
#define rep(i,x,n) for(int i=x; i<n; i++)
#define all(x) x.begin(), x.end()
template<class T> inline bool chmax(T &a, T b){if(a<b){a=b; return true;}return false;}
template<class T> inline bool chmin(T &a, T b){if(a>b){a=b; return true;}return false;}

int main(void){
  int n,r=0,g=0,b=0,ans;
  string s;
  cin >> n;
  cin >> s;

  rep(i,0,n){
    if(s[i]=='R')r++;
    if(s[i]=='G')g++;
    if(s[i]=='B')b++;
  }
  ans= r*g*b;
  rep(i,0,n-2){
    rep(d,1,n){
      int j,k;
      j=i+d;
      k=j+d;
      if(k>=n)break;
      if(s[i]!=s[j] && s[i]!=s[k] && s[j]!=s[k]){
        ans--;
      }
    }
  }

  cout << ans;

  return 0;
}