#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <array>
#include <queue>
#include <deque>
#include <map>
#include <set>
#include <sstream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <list>
#include <numeric>
#include <stack>
#include <iomanip>
#include <random>
#include <complex>
#include <functional>
#include <tuple>

using namespace std;

#define Rep(i,a,b) for(ll i = a; i < b; ++i)
#define rep(i,b) Rep(i,0,b)
#define allof(a) (a).begin(), (a).end()

#define Yes(q) ((q) ? "Yes" : "No")
#define YES(q) ((q) ? "YES" : "NO")
#define Possible(q) ((q) ? "Possible" : "Impossible")
#define POSSIBLE(q) ((q) ? "POSSIBLE" : "IMPOSSIBLE")

using ll = long long;

using pint = std::pair<int, int>;
using pll = std::pair<ll, ll>;

constexpr int inf = 1e9 + 7;
constexpr ll infll = 1ll << 60ll;
constexpr ll mod = 1e9 + 7;
// 0~3までは右左下上 4~7までは斜め
constexpr int dx[] = { 1, 0, -1, 0, 1, 1, -1, -1 };
constexpr int dy[] = { 0, -1, 0, 1, 1, -1, -1, 1 };

namespace {
    template<typename T> void chmax(T& a, T b) { a = std::max(a, b); }
    template<typename T> void chmin(T& a, T b) { a = std::min(a, b); }
    template<typename T> void chadd(T& a, T b) { a = a + b; }

    void Cout(long long x, const char* end = "\n") { std::cout << x << end; }
    template <typename T> void Cout(const T& x, const char* end = "\n") { std::cout << x << end; }
    template <typename T> void Cout(const std::vector<T>& x, const char* sep = " ", const char* end = "\n") { for (std::size_t i = 0, sz = x.size(); i < sz; i++) { std::cout << x[i] << (i == sz - 1 ? end : sep); } }

    // 標準入出力
    struct inp {
        std::size_t sz;
        inp(std::size_t _sz = 1) : sz(_sz) {}
        template <typename T> operator T () const { T a; std::cin >> a; return a; }
        template <typename T> operator std::vector<T>() const { vector<T> a(sz); for (std::size_t i = 0; i < sz; i++) std::cin >> a[i]; return a; }
        template <typename T, typename U> operator std::pair<T, U>() const { T f; U s; std::cin >> f >> s; return std::pair<T, U>(f, s); }
    };

    inp inp1; // input one
}

int main() {

    int n = inp1;
    string s = inp1;

    ll ans = 0;

    vector<vector<ll>> sum(3, vector<ll>(n + 1, 0));

    rep(i, n) {
        if (s[i] == 'R') sum[0][i]++;
        else if (s[i] == 'G') sum[1][i]++;
        else sum[2][i]++;
    }

    rep(i, n) {
        rep(j, 3) {
            sum[j][i + 1] += sum[j][i];
        }
    }

    rep(i, n) {
        Rep(j, i + 1, n) {
            if (s[i] == s[j]) continue;

            // kはjより大きい
            int dif = j - i;
            
            int id = 0;
            if (s[i] == 'R' && s[j] == 'G')id = 2;
            else if (s[i] == 'G' && s[j] == 'R') id = 2;
            else if (s[i] == 'R' && s[j] == 'B') id = 1;
            else if (s[i] == 'B' && s[j] == 'R') id = 1;
            else if (s[i] == 'G' && s[j] == 'B') id = 0;
            else if (s[i] == 'B' && s[j] == 'G') id = 0;

            ans += sum[id][n] - sum[id][j];

            if (j + dif < n && s[j + dif] != s[i] && s[j + dif] != s[j]) {
                --ans;
            }
        }
    }

    Cout(ans);

    return 0;
}


Measured memory_bytes: 3760