#include <bits/stdc++.h>
#define range(i, l, r) for(long long int (i) = (l); (i) < (r); (i)++)
#define reversed_range(i, l, r) for (long long int (i) = (r) - 1; (i) >= l; (i)--)
using namespace std;
template <typename T>
using vec = vector<T>;
using lint = long long;
using ulint = unsigned long long;
using pint = pair<int, int>;
using plint = pair<lint, lint>;

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

template <typename T>
ostream& operator <<(ostream& os, vec<T> v) {
    os << "[";
    if (v.size() == 0) return os << "]";
    for (int i = 0; i < v.size() - 1; i++) {
        os << v.at(i) << ", ";
    }
    return os << v.at(v.size() - 1) << "]";
}

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

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

template <typename K, typename V>
ostream& operator <<(ostream& os, map<K, V> m) {
    os << "{";
    if (m.begin() == m.end()) return os << "}";
    auto it_first_item = m.begin();
    os << it_first_item->first << ": " << it_first_item->second;
    for (auto it = ++it_first_item; it != m.end(); it++) {
        os << ", " << it->first << ": " << it->second;
    }
    return os << "}";
}

template <typename K, typename V>
ostream& operator <<(ostream& os, unordered_map<K, V> m) {
    os << "{";
    if (m.begin() == m.end()) return os << "}";
    auto it_first_item = m.begin();
    os << it_first_item->first << ": " << it_first_item->second;
    for (auto it = ++it_first_item; it != m.end(); it++) {
        os << ", " << it->first << ": " << it->second;
    }
    return os << "}";
}

lint pow(lint num, lint e, lint MOD) {
    lint res = 1;
    lint cur_num = num;
    while (e) {
        if (e & 1) {
            res *= cur_num;
            res %= MOD;
        }
        cur_num *= cur_num;
        cur_num %= MOD;
        e >>= 1;
    }
    return res;
}

int main() {
    cin.tie(0); cout.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
    lint N; string S; cin >> N >> S;
    vec<vec<lint>> pref_num_occurances(N, vec<lint>(3));
    unordered_map<char, lint> color_to_idx = { {'R', 0}, {'G', 1}, {'B', 2} };
    range(i, 0, N) {
        char c = S.at(i);
        lint idx = color_to_idx.at(c);
        pref_num_occurances[i][idx] += 1;
    }
    range(i, 1, N) {
        range(j, 0, 3) 
            pref_num_occurances.at(i).at(j) += pref_num_occurances.at(i - 1).at(j);
    }
    lint ans = 0;
    range(i, 0, N - 2) range(k, i + 2, N) {
        char c1 = S.at(i), c2 = S.at(k);
        if (c1 == c2) continue;
        char c3;
        if (c1 != 'R' and c2 != 'R') c3 = 'R';
        else if (c1 != 'G' and c2 != 'G') c3 = 'G';
        else c3 = 'B';
        lint num_occurances_c3 = pref_num_occurances.at(k - 1).at(color_to_idx.at(c3)) 
                               - pref_num_occurances.at(i).at(color_to_idx.at(c3));
        if ((i + k) % 2 == 0 and S.at((i + k) / 2) == c3) num_occurances_c3 -= 1;
        ans += num_occurances_c3;
    }
    cout << ans << "\n";
}

Measured memory_bytes: 3804