#include <bits/stdc++.h>
using namespace std;

// #define int long long // intで書いたけど心配なときにlong longに変換する
struct Fast {Fast(){std::cin.tie(0);ios::sync_with_stdio(false);}} fast;

/* short */
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define Fi first
#define Se second
#define ALL(v) begin(v), end(v)
#define RALL(v) rbegin(v), rend(v)
#define X real()
#define Y imag()

/* REPmacro */
#define REPS(i, a, n) for (ll i = (a); i < (ll)(n); ++i)
#define REP(i, n) REPS(i, 0, n)
#define RREP(i, n) REPS(i, 1, n + 1)
#define DEPS(i, a, n) for (ll i = (a); i >= (ll)(n); --i)
#define DEP(i, n) DEPS(i, n, 0)
#define EACH(i, n) for (auto&& i : n)

/* debug */
#define debug(x) cerr << x << " " << "(L:" << __LINE__ << ")" << '\n';

/* alias */
using ll = long long;
using ull = unsigned long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using pii = pair<int, int>;
using D = double;
using P = complex<D>;
using vs = vector<string>;
template <typename T> using PQ = priority_queue<T>;
template <typename T> using minPQ = priority_queue<T, vector<T>, greater<T>>;

/* const */
const int INF = 1001001001;
const ll LINF = 1001001001001001001ll;
const int MOD = 1e9 + 7;
const D EPS = 1e-9;
const int dx[] = {0, 1, 0, -1, 1, -1, 1, -1}, dy[] = {1, 0, -1, 0, 1, -1, -1, 1};

/* func */
inline bool inside(int y, int x, int H, int W) {return y >= 0 && x >= 0 && y < H && x < W;}
inline int in() {int x; cin >> x; return x;}
inline ll IN() {ll x; cin >> x; return x;}
inline vs split(const string& t, char c) {vs v; stringstream s(t); string b; while(getline(s, b, c)) v.eb(b); return v;}
template <typename T> inline bool chmin(T& a, const T& b) {if (a > b) a = b; return a > b;}
template <typename T> inline bool chmax(T& a, const T& b) {if (a < b) a = b; return a < b;}
template <typename T, typename S> inline void print(const pair<T, S>& p) {cout << p.first << " " << p.second << endl;}
template <typename T> inline void print(const T& x) {cout << x << endl;}
template <typename T, typename S> inline void print(const vector<pair<T, S>>& v) {for (auto&& p : v) print(p);}
template <typename T> inline void print(const vector<T>& v, string s = " ") {REP(i, v.size()) cout << v[i] << (i != (ll)v.size() - 1 ? s : "\n");}


signed main() {
    //my-code
    int N; cin >> N;
    string S; cin >> S;
    ll ans = 0;
    ll rcnt = 0;
    ll gcnt = 0;
    ll bcnt = 0;
    vector<ll> rv(N+1);
    vector<ll> gv(N+1);
    vector<ll> bv(N+1);
    rv[0] = 0;
    gv[0] = 0;
    bv[0] = 0;
    REP(i, N) {
        if (S[i] == 'R') rcnt++;
        if (S[i] == 'G') gcnt++;
        if (S[i] == 'B') bcnt++;
        rv[i+1] = rcnt;
        gv[i+1] = gcnt;
        bv[i+1] = bcnt;
    }
    if (N == 1 || N == 2) {
        cout << 0 << endl;
    }
    char ic, jc, kc;  // kc is "must be"
    REP(i, N-2) REPS(j, i+1, N-1) {
        ic = S[i]; jc = S[j];
        if(ic != jc) {
            if (ic != 'R' && jc != 'R') kc = 'R';
            if (ic != 'G' && jc != 'G') kc = 'G';
            if (ic != 'B' && jc != 'B') kc = 'B';

            if (kc == 'R') {
                ans += rcnt - rv[j+1];
            }
            if (kc == 'G') {
                ans += gcnt - gv[j+1];
            }
            if (kc == 'B') {
                ans += bcnt - bv[j+1];
            }

            if (j + (j-i) < N && S[j+(j-i)] == kc) ans--;
        }
    }

    cout << ans << endl;

    return 0;
}

// https://github.com/kurokoji/.cpp-Template/wiki テンプレートについて
// http://www.creativ.xyz/dump-cpp-652 dump()について
// https://gist.github.com/rigibun/7905920 色々

Measured memory_bytes: 3744