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

// clang-format off
#define  range(i, l, r) for (int i = (int)(l); i < (int)(r); ++(i))
#define rrange(i, l, r) for (int i = (int)(r) - 1; i >= (int)(l); --(i))

#define  whole(f, x, ...) ([&](decltype((x)) container) { return (f)(  begin(container),  end(container), ## __VA_ARGS__); })(x)
#define rwhole(f, x, ...) ([&](decltype((x)) container) { return (f)( rbegin(container), rend(container), ## __VA_ARGS__); })(x)

#define endl '\n'
#define debug(x) cerr << "(" << __LINE__ << ")" << #x << ": " << (x) << endl

using i32 = int;
using u32 = unsigned int;
using i64 = long long;
using u64 = unsigned long long;

// constexpr i32 mod   = 998244353;
constexpr i32 mod   = 1e9 + 7;
constexpr i32 inf   = 1001001001;
constexpr i64 infll = 1001001001001001001ll;

constexpr int dx[] = {0, -1, 1, 0, -1, 1, -1, 1}; 
constexpr int dy[] = {-1, 0, 0, 1, -1, -1, 1, 1};

struct IoSetup { IoSetup(int x = 15){ cin.tie(0); ios::sync_with_stdio(0); cout << fixed << setprecision(x); cerr << fixed << setprecision(x); } } iosetup;

template <typename T = i64> T input() { T x; cin >> x; return x; }

template <typename T> ostream &operator<<(ostream &os, vector<T> &v) { range(i, 0, v.size()) { os << v[i] << (i + 1 != v.size() ? " " : ""); } return os; } 
template <typename T> istream &operator>>(istream &is, vector<T> &v) { for (T &in : v) is >> in; return is; }

template <typename T1, typename T2> ostream &operator<<(ostream &os, pair<T1, T2> p) { os << "(" << p.first << ", " << p.second << ")"; return os; }
template <typename T1, typename T2> istream &operator>>(istream &is, pair<T1, T2> &p) { is >> p.first >> p.second; return is; }

template <typename T> vector<T> make_vector(size_t a, T b) { return vector<T>(a, b); }
template <typename... Ts> auto make_vector(size_t a, Ts... ts) { return vector<decltype(make_vector(ts...))>(a, make_vector(ts...)); }

template <typename T1, typename T2> inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }
template <typename T1, typename T2> inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); }
// clang-format on

void solver() {
    int N = input() + 1;
    string S = '.' + input<string>();

    vector< int > r(N), g(N), b(N);
    range(i, 1, N) {
        if (S[i] == 'R') {
            r[i]++;
            S[i] = '0';
        }
        if (S[i] == 'G') {
            g[i]++;
            S[i] = '1';
        }
        if (S[i] == 'B') {
            b[i]++;
            S[i] = '2';
        }

        r[i] += r[i - 1];
        g[i] += g[i - 1];
        b[i] += b[i - 1];
    }


    i64 ans = 0;
    range(i, 1, N) range(j, 1, i) {
        if (S[i] == S[j]) continue;
        
        bool f[3] = {1, 1, 1};
        f[S[i] - '0'] = f[S[j] - '0'] = false;
    
        int add;
        if (f[0]) {
            add = r[i] - r[j - 1];
            if ((i & 1) == (j & 1) && S[(i + j) / 2] - '0' == 0) add--;
        }
        if (f[1]) {
            add = g[i] - g[j - 1];
            if ((i & 1) == (j & 1) && S[(i + j) / 2] - '0' == 1) add--;
        }
        if (f[2]) {
            add = b[i] - b[j - 1];
            if ((i & 1) == (j & 1) && S[(i + j) / 2] - '0' == 2) add--;
        }

        ans += add;
    }
    
    cout << ans << endl;
}

signed main(int argc, char *argv[]) {
    solver();
}


Measured memory_bytes: 3668