#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vll = vector<ll>;
#define all(x) (x).begin(), (x).end()
#define fsp(x) cout << fixed << setprecision(x)
const ll inf = LLONG_MAX;
const long double pi = acos(-1);
void Yes() {cout << "Yes" << endl;}
void No() {cout << "No" << endl;}
void YES() {cout << "YES" << endl;}
void NO() {cout << "NO" << endl;}

int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);

	ll n;
	string s;
	cin >> n >> s;
	ll r = 0, g = 0, b = 0;
	for (ll i = 0; i < n; i++) {
		if (s[i] == 'R') r++;
		else if (s[i] == 'G') g++;
		else b++;
	}
	ll ans = r * g * b;
	for (ll i = 0; i < n - 2; i++) {
		for (ll j = i + 1; j < n - 1; j++) {
			ll k = 2 * j - i;
			if (k < n) {
				if (s[i] != s[j] && s[j] != s[k] && s[k] != s[i]) ans--;
			}
		}
	}
	cout << ans << endl;
}
