#include <iostream>
#include <algorithm>
#include <utility>
#include <string>
#include <vector>
#include <set>
#include <stack>
#include <queue>
#include <map>
#include <math.h>
#include <string.h>
#include <iomanip>
#include <numeric>
#include <cstdlib>
#include <cstdint>
#include <cmath>
#include <functional>
#include <limits>
#include <cassert>

using namespace std;

/* template */

using ll = long long;

void debug_out() { std::cout << endl; }
 
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cout << H << " ";
  debug_out(T...);
}

#ifdef LOCAL
#define debug(...) cout << "debug: "; debug_out(__VA_ARGS__)
#else
#define debug(...) 
#endif

#define rep(i, a, n) for (int i = (int)(a); i < (int)(n); i++)
#define rrep(i, a, n) for (int i = ((int)(n)-1); i >= (int)(a); i--)
#define Rep(i, a, n) for (long long i = (long long)(a); i< (long long)(n); i++)
#define RRep(i, a, n) for (long long i = ((long long)(n)-1); i>=(long long)(a); i--)
#define all(v) (v).begin(),(v).end()
#define rall(v) (v).rbegin(),(v).rend()

template <typename T>
std::ostream& operator<<(std::ostream& os, std::vector<T> vec) {
  for (std::size_t i = 0; i < vec.size(); i++)os << vec[i] << (i + 1 == vec.size() ? "" : " ");
  return os;
}

struct Edge{
    int to;
    int weight;
    Edge(int t, int w) : to(t), weight(w){ }
};

struct edge{
    int from;
    int to;
    int weight;
    edge(int f,int t,int w) : from(f), to(t), weight(w){ }
};


using Graph = vector<vector<Edge>>;
using graph = vector<vector<int>>;
using edges = vector<edge>;

template <class T>
inline bool chmin(T &a, T b){
    if (a > b){
        a = b;
        return true;
    }
    return false;
}

template <class T>
inline bool chmax(T &a, T b){
    if (a < b){
        a = b;
        return true;
    }
    return false;
}

template <class T>
T lcm(T a, T b){
    return (a*b)/gcd(a,b);
}

bool isPalindrome(string s){
    string t = s;
    reverse(all(t));
    return s==t;
}

constexpr ll INF = 1e18;

vector<int> dx = {-1,0,1,0};
vector<int> dy = {0,-1,0,1};

/* template */

vector<int> bfs(int s,const graph &g){
    int _size = g.size();
    vector<int> c(_size,-1);
    c[s] = 0;
    queue<int> que;
    que.push(s);
    while(!que.empty()){
        int x = que.front();
        que.pop();
        for(auto nx: g[x]){
            if(c[nx]<0){
                que.push(nx);
                c[nx] = c[x]+1;
            }
        }
    }
    return c;
}

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int n; string s; cin >> n >> s;
    vector<map<char,ll>> a(n);
    a[0][s[0]]++;
    rep(i,1,n){
        a[i]['R'] = a[i-1]['R'];
        a[i]['G'] = a[i-1]['G'];
        a[i]['B'] = a[i-1]['B'];
        a[i][s[i]]++;
    }
    ll ans = 0;
    rep(i,0,n){
        rep(j,i+1,n){
            if(s[i]==s[j]) continue;
            char flag = 'R';
            if((s[i]=='R' || s[i]=='G') && (s[j]=='R' || s[j]=='G')) flag = 'B';
            if((s[i]=='R' || s[i]=='B') && (s[j]=='R' || s[j]=='B')) flag = 'G';
            if(j+(j-i)<n && (s[j+(j-i)]!=s[j] && s[j+(j-i)]!=s[i]) && a[n-1][flag]!=a[j][flag]){
                ans += a[n-1][flag]-a[j][flag]-1;
            }
            else{
                ans += a[n-1][flag]-a[j][flag];
            }
        }
    }
    cout << ans << endl;
}

Measured memory_bytes: 4380