#include <bits/stdc++.h>
using namespace std;
#define REP(i,b,e) for(int i=(b);i<(e);++i)
#define RREP(i,b,e) for(int i=(b)-1;i>=e;--i)
#define rep(i,e) for(int i=0;i<(e);++i)

constexpr int MOD = 1000000007;
constexpr int INF = 1LL << 30;
constexpr long long LLINF = 1LL << 62;
constexpr double EPS = 1e-9;

struct Initializer {
  Initializer() {
    cin.tie(0);
    ios::sync_with_stdio(0);
    cout << fixed << setprecision(15) << boolalpha;
  }
} initializer;

template<typename T>
istream &operator>>(istream &is, vector<T> &vec) {
  for (T &x : vec) is >> x;
  return is;
}

template<typename T>
ostream &operator<<(ostream &os, const vector<T> &vec) {
  os << "[";
  for (auto it = vec.begin(); it != vec.end(); ++it) {
    if (it != vec.begin()) os << ", ";
    os << *it;
  }
  return os << "]";
}

template<typename T, typename U>
ostream &operator<<(ostream &os, const pair<T, U> &pa) {
  return os << "(" << pa.first << ", " << pa.second << ")";
}

template<typename Tuple, size_t N>
struct TuplePrinter {
  static void print(const Tuple &t) {
    TuplePrinter<Tuple, N-1>::print(t);
    cout << ", " << get<N-1>(t);
  }
};

template<typename Tuple>
struct TuplePrinter<Tuple, 1> {
  static void print(const Tuple &t) {
    cout << get<0>(t);
  }
};

template<typename... T>
ostream &operator<<(ostream &os, const tuple<T...> &tup) {
  os << "(";
  TuplePrinter<decltype(tup), sizeof...(T)>::print(tup);
  return os << ")";
}

template<typename T>
ostream &operator<<(ostream &os, const set<T> &se) {
  os << "{";
  for (auto it = se.begin(); it != se.end(); ++it) {
    if (it != se.begin()) os << ", ";
    os << *it;
  }
  return os << "}";
}

template<typename T, typename U>
ostream &operator<<(ostream &os, const map<T, U> &ma) {
  os << "{";
  for (auto it = ma.begin(); it != ma.end(); ++it) {
    if (it != ma.begin()) os << ", ";
    os << it->first << ": " << it->second;
  }
  return os << "}";
}

inline void print(void) { cout<<'\n'; }
template<class T> inline void print(const T &x) { cout<<x<<'\n'; }
template<class T, class... U> inline void print(const T &x, const U&... y) { cout<<x<<" "; print(y...); }
#define dump(...) cout<<#__VA_ARGS__<<": [L_"<<__LINE__<<"]"<<'\n'; print(__VA_ARGS__);cout<<'\n';

template<class T, class U>inline bool chmax(T &a, const U &b) { if(a<b){ a=b; return 1; } return 0; }
template<class T, class U>inline bool chmin(T &a, const U &b) { if(b<a){ a=b; return 1; } return 0; }


int main() {
  int n; cin>>n;
  string s; cin>>s;
  long long ans = 0;

  vector<int> r(n+1, 0), g(n+1, 0), b(n+1, 0);

  rep(i, n) {
    r[i] = r[i-1];
    b[i] = b[i-1];
    g[i] = g[i-1];
    if (s[i] == 'R') ++r[i];
    if (s[i] == 'G') ++g[i];
    if (s[i] == 'B') ++b[i];
  }

  REP(i, 1, n-1) {
    rep(j, i) {
      int diff = i-j;
      int k = i+diff;
      if (s[i] == 'R' and s[j] == 'G') {
        if (k < n and s[k] == 'B') ans += (b[n-1]-b[i]-1);
        else ans += (b[n-1]-b[i]);
      }
      if (s[i] == 'R' and s[j] == 'B') {
        if (k < n and s[k] == 'G') ans += (g[n-1]-g[i]-1);
        else ans += (g[n-1]-g[i]);
      }
      if (s[i] == 'G' and s[j] == 'R') {
        if (k < n and s[k] == 'B') ans += (b[n-1]-b[i]-1);
        else ans += (b[n-1]-b[i]);
      }
      if (s[i] == 'G' and s[j] == 'B') {
        if (k < n and s[k] == 'R') ans += (r[n-1]-r[i]-1);
        else ans += (r[n-1]-r[i]);
      }
      if (s[i] == 'B' and s[j] == 'G') {
        if (k < n and s[k] == 'R') ans += (r[n-1]-r[i]-1);
        else ans += (r[n-1]-r[i]);
      }
      if (s[i] == 'B' and s[j] == 'R') {
        if (k < n and s[k] == 'G') ans += (g[n-1]-g[i]-1);
        else ans += (g[n-1]-g[i]);
      }
    }
  }

  print(ans);

  return 0;
}

Measured memory_bytes: 3672