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

#define fastio 

#define ll long long
#define ff first
#define ss second
#define pb push_back
#define mp make_pair
#define ld long double
#define forn(low,high,i) for(i = low; i < high; i++)
#define forrev(high,low,i) for(i = high; i >= low; i--)
#define all(v) v.begin(),v.end()
#define decimal_digits cout << fixed << setprecision(15);

string to_string(string s) { return '"' + s + '"';}
string to_string(char s) { return string(1, s);}
string to_string(const char* s) { return to_string((string) s);}
string to_string(bool b) { return (b ? "true" : "false");}
template <typename A> string to_string(A);
template <typename A, typename B>string to_string(pair<A, B> p) {return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";}
template <typename A> string to_string(A v) {bool f = 1; string r = "{"; for (const auto &x : v) {if (!f)r += ", "; f = 0; r += to_string(x);} return r + "}";}
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) {cerr << " " << to_string(H); debug_out(T...);}
#define pr(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());

const int inf = 1e9;
const long long INF = 1e18;
const int mod = 1e9 + 7;
const int bit32 = log2(inf) + 3;
const int bit64 = log2(INF) + 3;

inline int add(long long a, long long b){a += b; if(a >= mod) a -= mod; return a;}
inline int sub(long long a, long long b){a -= b; if(a < 0) a += mod; return a;}
inline int mul(long long a, long long b){a %= mod; b %= mod; return (int)((long long) a * b % mod);}
inline int modexpo(long long a, long long b){int res = 1; while(b > 0){ if(b & 1) res = mul(res, a); a = mul(a, a); b /= 2;} return res;}
inline int divide(long long a, long long b){return mul(a, modexpo(b, mod - 2));}
inline int inv(long long a){return modexpo(a, mod - 2);}

clock_t time_p = clock();

void ktj(){
  time_p = clock() - time_p;
  cerr << "Time elapsed : " << (float)(time_p)/CLOCKS_PER_SEC << "\n";
}

void pre(){ // Reset each global variable (esp. for graphs)
  
}

void solve(){
  int n, i, j, k;
  string s;
  cin >> n >> s;
  vector<int> a;
  a.push_back(-1);
  for(auto c : s){
    if(c == 'R')
      a.push_back(0);
    if(c == 'G')
      a.push_back(1);
    if(c == 'B')
      a.push_back(2);
  }
  map<int, int> pos[3];

  vector<vector<int>> pre(n + 1, vector<int>(3, 0));

  for(i = 1; i <= n; i++){
    pos[a[i]][i] = 1;
    pre[i][a[i]] = 1;
  }

  for(i = n - 1; i >= 1; i--){
    for(j = 0; j < 3; j++){
      pre[i][j] += pre[i + 1][j];
    }
  }

  // pr(pre);
  // pr(pos[0], pos[1], pos[2]);

  long long ans = 0;

  for(i = 1; i <= n; i++){
    int x = a[i];
    for(j = 1; j < i; j++){
      int y = a[j];
      if(x != y){
        int z = 3 - x - y;
        ans += pre[i][z];
        k = 2*i - j;
        // pr(x, y, z, i, j, k);
        if(k > n)
          continue;
        ans -= pos[z][k];
      }
    }
  }

  cout << ans << '\n';

}

int main(){
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);cout.tie(NULL); 

  pre();

  int t = 1, T;
  // cin >> t;
  T = t;
  while(t--){
    // cout << "Case #" << T - t << ": ";
    solve();
  }

  ktj();
}


Measured memory_bytes: 4540