//#pragma GCC optimize("O2,no-stack-protector,unroll-loops,fast-math")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
//#pragma GCC target("avx,avx2,fma")
#include <bits/stdc++.h>
#include<thread>
//#include <boost/multiprecision/cpp_int.hpp>
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
using namespace std;
//using namespace boost::multiprecision;
using namespace __gnu_pbds;
template <typename T>
using os = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef long long ll;
typedef double ld;
#define ios ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
#define rep(i, begin, end) for (__typeof(end) i = (begin) - ((begin) > (end)); i != (end) - ((begin) > (end)); i += 1 - 2 * ((begin) > (end)))
#define pii pair<ll,ll>
#define vi vector<ll>
#define vii vector<pii>
#define mi map<ll,ll>
#define umi unordered_map<ll,ll,custom_hash>
#define all(a) (a).begin(),(a).end()
#define pb push_back
#define make make_pair
#define ff first
#define ss second
#define osl os<ll>
#define ospii os<pair<ll,ll> >
#define n_l '\n'
#define mem(a,b) memset(a,b,sizeof(a))
#define el "\n"
#define dbg(...) cout << "[" << #__VA_ARGS__ << "]: "; cout << to_string(__VA_ARGS__) << endl
template <typename T, size_t N> int SIZE(const T (&t)[N]){ return N; } template<typename T> int SIZE(const T &t){ return t.size(); } string to_string(const string s, int x1=0, int x2=1e9){ return '"' + ((x1 < s.size()) ? s.substr(x1, x2-x1+1) : "") + '"'; } string to_string(const char* s) { return to_string((string) s); } string to_string(const bool b) { return (b ? "true" : "false"); } string to_string(const char c){ return string({c}); } template<size_t N> string to_string(const bitset<N> &b, int x1=0, int x2=1e9){ string t = ""; for(int __iii__ = min(x1,SIZE(b)), __jjj__ = min(x2, SIZE(b)-1); __iii__ <= __jjj__; ++__iii__){ t += b[__iii__] + '0'; } return '"' + t + '"'; } template <typename A, typename... C> string to_string(const A (&v), int x1=0, int x2=1e9, C... coords); int l_v_l_v_l = 0, t_a_b_s = 0; template <typename A, typename B> string to_string(const pair<A, B> &p) { l_v_l_v_l++; string res = "(" + to_string(p.first) + ", " + to_string(p.second) + ")"; l_v_l_v_l--; return res; } template <typename A, typename... C> string to_string(const A (&v), int x1, int x2, C... coords) { int rnk = rank<A>::value; string tab(t_a_b_s, ' '); string res = ""; bool first = true; if(l_v_l_v_l == 0) res += n_l; res += tab + "["; x1 = min(x1, SIZE(v)), x2 = min(x2, SIZE(v)); auto l = begin(v); advance(l, x1); auto r = l; advance(r, (x2-x1) + (x2 < SIZE(v))); for (auto e = l; e != r; e = next(e)) { if (!first) { res += ", "; } first = false; l_v_l_v_l++; if(e != l){ if(rnk > 1) { res += n_l; t_a_b_s = l_v_l_v_l; }; } else{ t_a_b_s = 0; } res += to_string(*e, coords...); l_v_l_v_l--; } res += "]"; if(l_v_l_v_l == 0) res += n_l; return res; } void dbgm(){;} template<typename Heads, typename... Tails> void dbgm(Heads H, Tails... T){ cout << to_string(H) << " | "; dbgm(T...); }
#define dbgm(...) cout << "[" << #__VA_ARGS__ << "]: "; dbgm(__VA_ARGS__); cout << endl
clock_t time_p=clock();
std::istream& in(std::cin);
std::ostream& ot(std::cout);
ll mod=1e9+7;
void Auriel()
{
    time_p=clock()-time_p;
    cerr<<"Time Taken : "<<(float)(time_p)/CLOCKS_PER_SEC<<"\n";
}
struct custom_hash {
    static uint64_t splittpix64(uint64_t x) {

        x += 0x9e3779b97f4a7c15;
        x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
        x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
        return x ^ (x >> 31);
    }

    size_t operator()(uint64_t x) const {
        static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
        return splittpix64(x + FIXED_RANDOM);
    }
};
template <typename R>
void println(R r){
    for(auto i:r)
        cout<<i<<" ";
    cout<<endl;

}
template <typename R>
void print(R r){
    for(auto i:r)
        cout<<i<<el;
}
template <typename R>
void scnln(R &r){
    for(auto &i:r)
        cin>>i;
}
ll depth[400005],parent[400005];
void make_set(int v) {
    parent[v] = v;
    depth[v] = 0;
}
int find_set(int v) {
    if (v == parent[v])
        return v;
    return parent[v] = find_set(parent[v]);
}
void union_sets(int a, int b) {
    a = find_set(a);
    b = find_set(b);
    if (a != b) {
        if (depth[a] < depth[b])
            swap(a, b);
        parent[b] = a;
        if (depth[a] == depth[b])
            depth[a]++;
    }
}

int bfs(vi graph[],vi &visit,ll start) {
    queue<ll> q;
    q.push(start);
    visit[start]=1;
    while (q.size() != 0) {
        ll p = q.front();
        q.pop();
        if (visit[p] == 1) continue;
        //visit[p] = 1;
        for (auto child:graph[p]) {
            if (!visit[child]) {
                visit[child]=1;
                q.push(child);
            }
        }
    }
}
vi level(ll(2e5+2),0); ll st[200001],ft[200001]; ll tt=0;
void dfs(vi graph[],vi &visit,ll start) {
    visit[start] = 1;
    st[start]=tt; tt++;
    for (auto child:graph[start]) {
        if (!visit[child]) {
            level[child]=level[start]+1;
            parent[child]=start;
            dfs(graph, visit, child);
        }
    }
    ft[start]=tt;
}

ll binexp(ll a, ll b,ll md) {
    if (b == 0)
        return 1;
    ll res = binexp(a, b / 2,md);
    if (b % 2)
        return (((res %md) * res%md)%md * a)%md;
    else
        return (res * res)%md;
}
//template <typename T>
//T inverse(T a, T m) {
//    T u = 0, v = 1;
//    while (a != 0) {
//        T t = m / a;
//        m -= t * a;
//        swap(a, m);
//        u -= t * v;
//        swap(u, v);
//    }
//    assert(m == 1);
//    return u;
//}
//
//template <typename T>
//class Modular {
//public:
//    using Type = typename decay<decltype(T::value)>::type;
//
//    constexpr Modular() : value() {}
//    template <typename U>
//    Modular(const U& x) {
//        value = normalize(x);
//    }
//
//    template <typename U>
//    static Type normalize(const U& x) {
//        Type v;
//        if (-mod() <= x && x < mod())
//            v = static_cast<Type>(x);
//        else
//            v = static_cast<Type>(x % mod());
//        if (v < 0) v += mod();
//        return v;
//    }
//
//    const Type& operator()() const { return value; }
//    template <typename U>
//    explicit operator U() const {
//        return static_cast<U>(value);
//    }
//    constexpr static Type mod() { return T::value; }
//
//    Modular& operator+=(const Modular& other) {
//        if ((value += other.value) >= mod()) value -= mod();
//        return *this;
//    }
//    Modular& operator-=(const Modular& other) {
//        if ((value -= other.value) < 0) value += mod();
//        return *this;
//    }
//    template <typename U>
//    Modular& operator+=(const U& other) {
//        return *this += Modular(other);
//    }
//    template <typename U>
//    Modular& operator-=(const U& other) {
//        return *this -= Modular(other);
//    }
//    Modular& operator++() { return *this += 1; }
//    Modular& operator--() { return *this -= 1; }
//    Modular operator++(int) {
//        Modular result(*this);
//        *this += 1;
//        return result;
//    }
//    Modular operator--(int) {
//        Modular result(*this);
//        *this -= 1;
//        return result;
//    }
//    Modular operator-() const { return Modular(-value); }
//
//    template <typename U = T>
//    typename enable_if<is_same<typename Modular<U>::Type, int>::value,
//            Modular>::type&
//    operator*=(const Modular& rhs) {
//#ifdef _WIN32
//        uint64_t x = static_cast<int64_t>(value) * static_cast<int64_t>(rhs.value);
//    uint32_t xh = static_cast<uint32_t>(x >> 32), xl = static_cast<uint32_t>(x),
//             d, m;
//    asm("divl %4; \n\t" : "=a"(d), "=d"(m) : "d"(xh), "a"(xl), "r"(mod()));
//    value = m;
//#else
//        value = normalize(static_cast<int64_t>(value) *
//                          static_cast<int64_t>(rhs.value));
//#endif
//        return *this;
//    }
//    template <typename U = T>
//    typename enable_if<is_same<typename Modular<U>::Type, int64_t>::value,
//            Modular>::type&
//    operator*=(const Modular& rhs) {
//        int64_t q = static_cast<int64_t>(static_cast<long double>(value) *
//                                         rhs.value / mod());
//        value = normalize(value * rhs.value - q * mod());
//        return *this;
//    }
//    template <typename U = T>
//    typename enable_if<!is_integral<typename Modular<U>::Type>::value,
//            Modular>::type&
//    operator*=(const Modular& rhs) {
//        value = normalize(value * rhs.value);
//        return *this;
//    }
//
//    Modular& operator/=(const Modular& other) {
//        return *this *= Modular(inverse(other.value, mod()));
//    }
//
//    template <typename U>
//    friend bool operator==(const Modular<U>& lhs, const Modular<U>& rhs);
//
//    template <typename U>
//    friend bool operator<(const Modular<U>& lhs, const Modular<U>& rhs);
//
//    template <typename U>
//    friend std::istream& operator>>(std::istream& stream, Modular<U>& number);
//
//private:
//    Type value;
//};
//
//template <typename T>
//bool operator==(const Modular<T>& lhs, const Modular<T>& rhs) {
//    return lhs.value == rhs.value;
//}
//template <typename T, typename U>
//bool operator==(const Modular<T>& lhs, U rhs) {
//    return lhs == Modular<T>(rhs);
//}
//template <typename T, typename U>
//bool operator==(U lhs, const Modular<T>& rhs) {
//    return Modular<T>(lhs) == rhs;
//}
//
//template <typename T>
//bool operator!=(const Modular<T>& lhs, const Modular<T>& rhs) {
//    return !(lhs == rhs);
//}
//template <typename T, typename U>
//bool operator!=(const Modular<T>& lhs, U rhs) {
//    return !(lhs == rhs);
//}
//template <typename T, typename U>
//bool operator!=(U lhs, const Modular<T>& rhs) {
//    return !(lhs == rhs);
//}
//
//template <typename T>
//bool operator<(const Modular<T>& lhs, const Modular<T>& rhs) {
//    return lhs.value < rhs.value;
//}
//
//template <typename T>
//Modular<T> operator+(const Modular<T>& lhs, const Modular<T>& rhs) {
//    return Modular<T>(lhs) += rhs;
//}
//template <typename T, typename U>
//Modular<T> operator+(const Modular<T>& lhs, U rhs) {
//    return Modular<T>(lhs) += rhs;
//}
//template <typename T, typename U>
//Modular<T> operator+(U lhs, const Modular<T>& rhs) {
//    return Modular<T>(lhs) += rhs;
//}
//
//template <typename T>
//Modular<T> operator-(const Modular<T>& lhs, const Modular<T>& rhs) {
//    return Modular<T>(lhs) -= rhs;
//}
//template <typename T, typename U>
//Modular<T> operator-(const Modular<T>& lhs, U rhs) {
//    return Modular<T>(lhs) -= rhs;
//}
//template <typename T, typename U>
//Modular<T> operator-(U lhs, const Modular<T>& rhs) {
//    return Modular<T>(lhs) -= rhs;
//}
//
//template <typename T>
//Modular<T> operator*(const Modular<T>& lhs, const Modular<T>& rhs) {
//    return Modular<T>(lhs) *= rhs;
//}
//template <typename T, typename U>
//Modular<T> operator*(const Modular<T>& lhs, U rhs) {
//    return Modular<T>(lhs) *= rhs;
//}
//template <typename T, typename U>
//Modular<T> operator*(U lhs, const Modular<T>& rhs) {
//    return Modular<T>(lhs) *= rhs;
//}
//
//template <typename T>
//Modular<T> operator/(const Modular<T>& lhs, const Modular<T>& rhs) {
//    return Modular<T>(lhs) /= rhs;
//}
//template <typename T, typename U>
//Modular<T> operator/(const Modular<T>& lhs, U rhs) {
//    return Modular<T>(lhs) /= rhs;
//}
//template <typename T, typename U>
//Modular<T> operator/(U lhs, const Modular<T>& rhs) {
//    return Modular<T>(lhs) /= rhs;
//}
//
//template <typename T, typename U>
//Modular<T> power(const Modular<T>& a, const U& b) {
//    assert(b >= 0);
//    Modular<T> x = a, res = 1;
//    U p = b;
//    while (p > 0) {
//        if (p & 1) res *= x;
//        x *= x;
//        p >>= 1;
//    }
//    return res;
//}
//
//template <typename T>
//std::ostream& operator<<(std::ostream& stream, const Modular<T>& number) {
//    return stream << number();
//}
//
//template <typename T>
//std::istream& operator>>(std::istream& stream, Modular<T>& number) {
//    typename common_type<typename Modular<T>::Type, int64_t>::type x;
//    stream >> x;
//    number.value = Modular<T>::normalize(x);
//    return stream;
//}
//
///*
//using ModType = int;
//struct VarMod { static ModType value; };
//ModType VarMod::value;
//ModType& md = VarMod::value;
//using Mint = Modular<VarMod>;
//*/
//constexpr ll md = 4;  // 1e9 + 7; // 998244353;
//using Mint = Modular<std::integral_constant<decay<decltype(md)>::type, md>>;
int main() {
    ios
    ll n; in>>n; map<char,os<ll>> mp;
    string s; in>>s; ll idx=0;
    for(auto i:s){
        mp[i].insert(idx);
        idx++;
    }
    ll ans=0;
    rep(i,0,n){
        rep(j,i+1,n){
            if(s[i]!=s[j]){
                char c;
                if((s[i]=='R'&&s[j]=='G')||(s[i]=='G'&&s[j]=='R'))
                    c='B';
                else if((s[i]=='R'&&s[j]=='B')||(s[i]=='B'&&s[j]=='R'))
                    c='G';
                else if((s[i]=='B'&&s[j]=='G')||(s[i]=='G'&&s[j]=='B'))
                    c='R';
                idx=j+1;
                ans+=mp[c].size()-mp[c].order_of_key(idx);
                if(mp[c].find(j+j-i)!=mp[c].end())
                    ans--;

            }
        }
    }
    ot<<ans<<el;
    Auriel();



}


Measured memory_bytes: 5108