#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using VI = vector<int>;
using VL = vector<ll>;
using VS = vector<string>;
using VVI = vector<VI>;
using VVL = vector<VL>;
using PII = std::pair<int, int>;
using PLL = std::pair<ll, ll>;

#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repr(i, n) for (int i = (int)(n)-1; i >= 0; i--)
#define rep2(i, s, n) for (int i = (s); i < (int)(n); i++)
#define rep3(i, s, n, d) for (int i = (s); i < (int)(n); i += (d))
#define allpt(v) (v).begin(), (v).end()
#define allpt_c(v) (v).cbegin(), (v).cend()
#define allpt_r(v) (v).rbegin(), (v).rend()

const int mod = 1e9 + 7, mod2 = 998244353, mod3 = 1e9 + 9;
const ll inf = 1e18;

const string wsp = " ";
const string tb = "\t";
const string rt = "\n";

template <typename T>
void show1dvec(const vector<T> &v)
{
    if (v.size() == 0)
        return;
    int n = v.size() - 1;
    rep(i, n) cout << v[i] << wsp;
    cout << v[n] << rt;

    return;
}

template <typename T>
void show2dvec(const vector<vector<T>> &v)
{
    int n = v.size();
    rep(i, n) show1dvec(v[i]);
}

template <typename T, typename S>
void show1dpair(const vector<pair<T, S>> &v)
{
    int n = v.size();
    rep(i, n) cout << v[i].first << wsp << v[i].second << rt;
    return;
}

template <typename T, typename S>
void pairzip(const vector<pair<T, S>> &v, vector<T> &t, vector<T> &s)
{
    int n = v.size();
    rep(i, n)
    {
        t.push_back(v[i].first);
        s.push_back(v[i].second);
    }
    return;
}

template <typename T>
void maxvec(vector<T> &v)
{
    T s = v[0];
    int n = v.size();
    rep(i, n - 1)
    {
        if (s > v[i + 1])
        {
            v[i + 1] = s;
        }
        s = v[i + 1];
    }
}

template <typename T, typename S>
bool myfind(T t, S s)
{
    return find(t.cbegin(), t.cend(), s) != t.cend();
}

bool check(int y, int x, int h, int w)
{
    return 0 <= y && y < h && 0 <= x && x < w;
}

VL cumsum(const VL &v)
{
    int s = 0;
    VL ret = {0};

    rep(i, v.size())
    {
        s += v[i];
        ret.push_back(s);
    }
    return ret;
}

bool iskadomatsu(int a, int b, int c)
{
    return (a != b && b != c && c != a) && ((a > b && b < c) || (a < b && b > c));
}

void shave(vector<int> &v, int k, int n)
{
    vector<int> x, y;
    int n_sq = sqrt(n) + 1;
    for (int i = 3; i < n + 1; i += 2)
    {
        x.push_back(i);
    }
    for (int i = 3; i < n_sq; i += 2)
    {
        for (auto itr = x.cbegin(); itr != x.cend(); itr++)
        {
            if (*itr == i || *itr % i != 0)
                y.push_back(*itr);
        }
        x.clear();
        x = y;
        y.clear();
    }

    if (n >= 2 && k <= 2)
        v.push_back(2);
    for (auto itr = x.cbegin(); itr != x.cend(); itr++)
    {
        if (*itr >= k)
            v.push_back(*itr);
    }
}

bool cond1(const VI &num)
{
    bool res{true};
    rep(i, 3) rep(j, 2)
    {
        if (num[3 * i + j] > num[3 * i + j + 1])
            res = false;
    }
    rep(i, 2) rep(j, 3)
    {
        if (num[3 * i + j] > num[3 * i + j + 3])
            res = false;
    }
    return res;
}

void cond2(const int &n, const VI &num, const VI &a, set<VI> &ans_list)
{
    int maxnum = 0;
    VI use_num;
    rep(i, 3)
    {
        rep(j, a[i])
        {
            maxnum = max(maxnum, num[3 * i + j]);
            use_num.push_back(num[3 * i + j]);
        }
    }
    if (maxnum == n - 1)
        ans_list.insert(use_num);
}



int main()
{

#ifdef DEBUG
    cout << "DEBUG MODE" << endl;
    ifstream in("input.txt"); //for debug
    cin.rdbuf(in.rdbuf());    //for debug
#endif

    int n, r, g, b, p;
    string s;
    cin >> n >> s;
    ll ans{0};

    VI r1(n), r2(n), g1(n), g2(n), b1(n), b2(n);

    r = g = b = 0;
    rep(i, n)
    {
        if (s[i] == 'R')
            r++;
        if (s[i] == 'G')
            g++;
        if (s[i] == 'B')
            b++;
        r1[i] = r;
        b1[i] = b;
        g1[i] = g;
    }
    r = g = b = 0;
    repr(i, n)
    {
        if (s[i] == 'R')
            r++;
        if (s[i] == 'G')
            g++;
        if (s[i] == 'B')
            b++;
        r2[i] = r;
        b2[i] = b;
        g2[i] = g;
    }

    // VVI allrgb{r1, r2, g1, g2, b1, b2};
    // show2dvec(allrgb);

    rep(i, n)
    {
        if (s[i] == 'R')
        {
            ans += g1[i] * b2[i] + b1[i] * g2[i];
        }
        if (s[i] == 'G')
        {
            ans += r1[i] * b2[i] + b1[i] * r2[i];
        }
        if (s[i] == 'B')
        {
            ans += g1[i] * r2[i] + r1[i] * g2[i];
        }
        p = min(i, n - i - 1);
        rep2(j, 1, p + 1)
        {
            if(s[i] != s[i - j] && s[i] != s[i + j] && s[i + j] != s[i - j]) ans--;
        }
        // rep(j, min(i, n - i - 1))
        //     cout << j << rt;
    }

    cout << ans << rt;
    return 0;
}


Measured memory_bytes: 3728