#include <bits/stdc++.h>
// #include <boost/multiprecision/cpp_dec_float.hpp>
// #include <boost/multiprecision/cpp_int.hpp>
using namespace std;

/***** type *****/
using ll = long long;
using ld = long double;
// using ml = boost::multiprecision::cpp_int;
// using md = boost::multiprecision::cpp_dec_float_100;
using pll = pair<long long, long long>;
template <class T> using vt = vector<T>;
template <class T> using vvt = vector<vector<T>>;
template <class T> using vvvt = vector<vector<vector<T>>>;
template <class T> using uset = unordered_set<T>;
template <class T1, class T2> using umap = unordered_map<T1, T2>;

/***** define *****/
#define all(c) (c).begin(), (c).end()            // begin to end
#define coutd cout << fixed << setprecision(10)  // cout double
#define rep(i, b, e) for (ll i = b; i < e; i++)  // repeat
#define repr(i, b, e) for (ll i = b; e < i; i--) // repeat reverse
#define pair NyaaPair                            // nyaa pair
#define first f                                  // pair::first
#define second s                                 // pair::second
/***** const value *****/
#define llong_max 9223372036854775807 // 9 * 10^18
#define ldbl_max 1.79769e+308         // 1.7 * 10^308
#define pi 3.1415926535897932         // 3.14 ...
#define loop_end 9223372036854775806  // LLONG_MAX-1
/***** for each macro *****/
#define fori(i, ...)                                                           \
    if (ll i = -1)                                                             \
        for (__VA_ARGS__)                                                      \
            if (i++, true)
#define each(i, e, c) fori(i, auto &e : c)
#define forir(i, v, ...)                                                       \
    if (ll i = (ll)v.size())                                                   \
        for (__VA_ARGS__)                                                      \
            if (i--, true)
#define eachr(i, e, c) forir(i, auto e = c.rbegin(); e != c.rend(); ++e)

/***** lambda *****/
auto Count = [] // long long count value
    (auto b, auto e, auto x) { return (ll)count(b, e, x); };
auto CtoL = [] // char to number
    (auto c) { return (ll)(c - '0'); };
auto CeilD = [] // long double ceiling div
    (auto a, auto b) { return (ll)ceil((ld)a / (ld)b); };
auto Fix = [] // fix value
    (auto b, auto e, auto fix) {
        for (auto it = b; it != e; ++it)
            *it += fix;
    };
auto LtoC = [] // number to char
    (auto n) { return (char)('0' + n); };
auto Pow = [] // long long pow
    (auto a, auto b) { return (ll)pow(a, b); };
auto Pow2 = [] // long long pow2
    (auto n) { return (1LL << n); };
auto Pow10 = [] // long long pow10
    (auto n) { return (ll)pow(10, n); };
auto Size = [] // long long collection size
    (auto &c) { return (ll)(c).size(); };
auto Sum = [] // long long accumulate
    (auto b, auto e) { return accumulate(b, e, 0LL); };

/***** template *****/
template <class T>
void MakeVVT(ll ys, ll xs, vvt<T> &v,
             T fill = T()) { // vector<vector<T>> resize + fill
    v.resize(ys);
    rep(y, 0, ys) v[y].resize(xs, fill);
}
template <class T>
void MakeVVVT(ll zs, ll ys, ll xs, vvvt<T> &v,
              T fill = T()) { // vector<vector<vector<T>>> resize + fill
    v.resize(zs);
    rep(z, 0, zs) MakeVVT(ys, xs, v[z], fill);
}
template <class T>
void InputVT(ll xs, vt<T> &v,
             T fix = T()) { // input vector<T> (T != struct) + fix
    v.resize(xs);
    rep(i, 0, xs) {
        cin >> v[i];
        v[i] += fix;
    }
}
template <class T>
void InputVVT(ll ys, ll xs, vvt<T> &v,
              T fix = T()) { // input vector<vector<T>> (T != struct) + fix
    MakeVVT(ys, xs, v, fix);
    rep(y, 0, ys) rep(x, 0, xs) {
        cin >> v[y][x];
        v[y][x] += fix;
    }
}
template <class T>
void InputVVVT(
    ll zs, ll ys, ll xs, vvvt<T> &v,
    T fix = T()) { // input vector<vector<vector<T>>> (T != struct) + fix
    v.resize(zs);
    rep(z, 0, zs) InputVVT(ys, xs, v[z], fix);
}
template <class T1, class T2> struct NyaaPair { // nyaa pair template
    T1 f;
    T2 s;
};
template <class T1, class T2>
bool operator<(const NyaaPair<T1, T2> &l,
               const NyaaPair<T1, T2> &r) { // nyaa pair template operator <
    return (l.f != r.f) ? l.f < r.f : l.s < r.s;
}
template <class T1, class T2>
bool operator>(const NyaaPair<T1, T2> &l,
               const NyaaPair<T1, T2> &r) { // nyaa pair template operator >
    return (l.f != r.f) ? l.f > r.f : l.s > r.s;
}

/**************************************/
/********** BEGIN OF NYA LIB **********/
/**************************************/

namespace NyaGadget {}

/**************************************/
/*********** END OF NYA LIB ***********/
/**************************************/

using namespace NyaGadget;
// using mll = ModLL< 1000000007 >;
// using mll = ModLL< 998244353 >;

int main(void) {
    ll N;
    cin >> N;
    string S;
    cin >> S;

    map<char, ll> count;
    each(i, e, S) count[e]++;

    ll ans = count['R'] * count['G'] * count['B'];
    rep(w, 1, Size(S)) rep(m, 1, Size(S)) {
        if (m - w < 0 || Size(S) <= m + w)
            continue;
        if (S[m] != S[m - w] && S[m] != S[m + w] && S[m - w] != S[m + w]) {
            ans--;
        }
    }
    cout << ans << endl;

    return 0;
}


Measured memory_bytes: 3596