/*

  "With age, comes wisdom. With travel, comes understanding.
   Remember that happiness is a way of travel – not a destination"

*/

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;

#define int            long long int
#define F              first
#define S              second
#define pb             push_back
#define si             set <int>
#define vi             vector <int>
#define pii            pair <int, int>
#define vpi            vector <pii>
#define vpp            vector <pair<int, pii>>
#define mii            map <int, int>
#define mpi            map <pii, int>
#define spi            set <pii>
#define endl           "\n"
#define sz(x)          ((int) x.size())
#define all(p)         p.begin(), p.end()
#define double         long double
#define que_max        priority_queue <int>
#define que_min        priority_queue <int, vi, greater<int>>
#define bug(...)       __f (#__VA_ARGS__, __VA_ARGS__)
#define print(a)       for(auto x : a) cout << x << " "; cout << endl
#define print1(a)      for(auto x : a) cout << x.F << " " << x.S << endl
#define print2(a,x,y)  for(int i = x; i < y; i++) cout<< a[i]<< " "; cout << endl

inline int power(int a, int b)
{
     int x = 1;
     while (b)
     {
          if (b & 1) x *= a;
          a *= a;
          b >>= 1;
     }
     return x;
}

typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> Set;

template <typename Arg1>
void __f (const char* name, Arg1&& arg1) { cout << name << " : " << arg1 << endl; }
template <typename Arg1, typename... Args>
void __f (const char* names, Arg1&& arg1, Args&&... args)
{
     const char* comma = strchr (names + 1, ',');
     cout.write (names, comma - names) << " : " << arg1 << " | "; __f (comma + 1, args...);
}

const int N = 200005;
int a[N], n, m, k;
string s;

Set r, b, g;

void solve()
{
     cin >> n;
     cin >> s;

     for (int i = 0; i < n; i++)
     {
          if (s[i] == 'R')
               r.insert(i);
          else if (s[i] == 'B')
               b.insert(i);
          else
               g.insert(i);
     }
     int ans = 0;

     for (int i = 0; i < n; i++)
     {
          if (s[i] == 'R')
          {
               int cur = *r.begin();
               r.erase(cur);
               for (auto x : b)
               {
                    int tot = sz(g) - g.order_of_key(x);
                    int d = x - cur;

                    if (g.find(x + d) != g.end())
                         tot--;

                    ans += tot;
               }
               for (auto x : g)
               {
                    int tot = sz(b) - b.order_of_key(x);
                    int d = x - cur;

                    if (b.find(x + d) != b.end())
                         tot--;

                    ans += tot;
               }
          }
          else if (s[i] == 'B')
          {
               int cur = *b.begin();
               b.erase(cur);
               for (auto x : r)
               {
                    int tot = sz(g) - g.order_of_key(x);
                    int d = x - cur;

                    if (g.find(x + d) != g.end())
                         tot--;

                    ans += tot;
               }
               for (auto x : g)
               {
                    int tot = sz(r) - r.order_of_key(x);
                    int d = x - cur;

                    if (r.find(x + d) != r.end())
                         tot--;

                    ans += tot;
               }
          }
          else
          {
               int cur = *g.begin();
               g.erase(cur);
               for (auto x : r)
               {
                    int tot = sz(b) - b.order_of_key(x);
                    int d = x - cur;

                    if (b.find(x + d) != b.end())
                         tot--;

                    ans += tot;
               }
               for (auto x : b)
               {
                    int tot = sz(r) - r.order_of_key(x);
                    int d = x - cur;

                    if (r.find(x + d) != r.end())
                         tot--;

                    ans += tot;
               }
          }
     }

     cout << ans;

}

int32_t main()
{
     ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

#ifndef ONLINE_JUDGE
     freopen("input.txt",  "r",  stdin);
     freopen("output.txt", "w", stdout);
#endif

     cout << setprecision(9) << fixed;
     clock_t z = clock();
     solve();
     cerr << "Run Time : " << ((double)(clock() - z) / CLOCKS_PER_SEC);

     return 0;
}

Measured memory_bytes: 4016