#include <bits/stdc++.h>
#ifdef LOCAL_DEBUG
#define DEBUG 1
#define CERR if(DEBUG) cerr
#define MACRO(_1,_2,_3,_4,_5,_6,_7,_8,_9,_10,NAME,...) NAME
#define pr(...) CERR<<MACRO(__VA_ARGS__,pr10,pr9,pr8,pr7,pr6,pr5,pr4,pr3,pr2,pr1)(__VA_ARGS__)<<endl
#define pr1(a) (#a)<<"="<<(a)<<" "
#define pr2(a,b) pr1(a)<<pr1(b)
#define pr3(a,b,c) pr1(a)<<pr2(b,c)
#define pr4(a,b,c,d) pr1(a)<<pr3(b,c,d)
#define pr5(a,b,c,d,e) pr1(a)<<pr4(b,c,d,e)
#define pr6(a,b,c,d,e,f) pr1(a)<<pr5(b,c,d,e,f)
#define pr7(a,b,c,d,e,f,g) pr1(a)<<pr6(b,c,d,e,f,g)
#define pr8(a,b,c,d,e,f,g,h) pr1(a)<<pr7(b,c,d,e,f,g,h)
#define pr9(a,b,c,d,e,f,g,h,i) pr1(a)<<pr8(b,c,d,e,f,g,h,i)
#define pr10(a,b,c,d,e,f,g,h,i,j) pr1(a)<<pr9(b,c,d,e,f,g,h,i,j)
#define prArr(a){CERR<<(#a)<<"={";int i=0;for(auto t:(a))CERR<<(i++?", ":"")<<t;CERR<<"}"<<endl;}
#else
#define DEBUG 0
#define pr(...)
#define prArr(a)
#endif
using namespace std;
using Int = long long;
using _int = int;
using ll = long long;
using Double = long double;
const Int INF = (1LL<<60)+1e9; // ~ 1.15 * 1e18
const Int mod = (1e9)+7;
const Double EPS = 1e-8;
const Double PI = 6.0 * asin((Double)0.5);
using P = pair<Int,Int>;
template<class T> T Max(T &a,T b){return a=max(a,b);}
template<class T> T Min(T &a,T b){return a=min(a,b);}
template<class T1, class T2> ostream& operator<<(ostream& o,pair<T1,T2> p){return o<<"("<<p.first<<","<<p.second<<")";}
template<class T1, class T2, class T3> ostream& operator<<(ostream& o,tuple<T1,T2,T3> t){return o<<"("<<get<0>(t)<<","<<get<1>(t)<<","<<get<2>(t)<<")";}
template<class T1, class T2> istream& operator>>(istream& i,pair<T1,T2> &p){return i>>p.first>>p.second;}
template<class T> ostream& operator<<(ostream& o,vector<T> a){Int i=0;for(T t:a)o<<(i++?" ":"")<<t;return o;}
template<class T> istream& operator>>(istream& i,vector<T> &a){for(T &t:a)i>>t;return i;}
//INSERT ABOVE HERE

template<typename T>
class CumulativeSum{
public:
  Int n;
  vector<T> sum;
  vector<T> A;
  Int added;
  CumulativeSum():n(-1),added(0){}
  CumulativeSum(Int n):n(n), sum(n+1), A(n+1),added(0){}
  CumulativeSum(const vector<T> &B):n(B.size()), sum(n+1), A(n+1),added(0){
    for(Int i=1;i<=n;i++) sum[i] = sum[i-1] + B[i-1];
  }

  void apply(){
    for(Int i=1;i<=n;i++) A[i] = A[i] + A[i-1];
    for(Int i=1;i<=n;i++) A[i] = A[i] + A[i-1];
    for(Int i=1;i<=n;i++) sum[i] = sum[i] + A[i-1];
    added = 0; A.clear(); A.resize(n+1);
  }

  //[l, r)にxを加算
  void add(Int l, Int r, T x){
    added = 1;
    assert(l <= r && 0 <= l && r <= n);
    A[l] = A[l] + x;
    A[r] = A[r] - x;
  }

  //[l, r)の和を得る
  T get(Int l,Int r){
    assert(l<=r && 0<=l && r<=n);
    if(added) apply();
    return sum[r] - sum[l];
  }
};


signed main(){
  srand((unsigned)time(NULL));
  cin.tie(0);
  ios_base::sync_with_stdio(0);
  cout << fixed << setprecision(12);

  Int N;
  cin>>N;

  string S;
  cin>>S;

  vector<Int> R(N), G(N), B(N);
  for(Int i=0;i<N;i++){
    R[i] = S[i] == 'R';
    G[i] = S[i] == 'G';
    B[i] = S[i] == 'B';
  }

  CumulativeSum<Int> sR(R), sG(G), sB(B);
  auto calc = [&](auto &A, auto&B, Int i)->Int{
    Int a = A.get(0, i) * B.get(i, N);
    Int b = B.get(0, i) * A.get(i, N);
    Int c = 0;
    for(Int j=1;j<=N;j++){
      if(i - j < 0 || i + j >= N) break;
      if(S[i] != S[i-j] && S[i] != S[i+j] && S[i-j] != S[i+j]) c++;
    }
    return a + b - c;
  };
  Int ans = 0;
  for(Int i=1;i<N-1;i++){
    char x = S[i];
    if(x == 'R') ans += calc(sG, sB, i);
    if(x == 'G') ans += calc(sR, sB, i);
    if(x == 'B') ans += calc(sG, sR, i);
  }

  cout<<ans<<endl;


  return 0;
}


Measured memory_bytes: 3796