# include <bits/stdc++.h>
# define speed ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
# define int long long
  
using namespace std;
  
const int N = 1e3 + 7;
const int INF = 1e18;
const int mod = 1e9 + 7; 

int R[N], G[N], B[N], n;

string s;

int check( int k, char c ) {

	if ( k >= n ) {
		return 0;
	}
	return ( s[k] == c );
}
  
int32_t main() {
    speed;
	cin >> n;
	cin >> s;

	for ( int i = n - 1; i >= 0; i-- ) {

		R[i] += R[i + 1];
		G[i] += G[i + 1];
		B[i] += B[i + 1];
		
		if ( s[i] == 'R' ) {
			R[i]++;
		}
		if ( s[i] == 'G' ) {
			G[i]++;
		}
		if ( s[i] == 'B' ) {
			B[i]++;
		}
	}
	int ans = 0;

	for ( int i = 0; i < n; i++ ) {
		for ( int j = i + 1; j < n; j++ ) {

			
			if ( s[i] == s[j] ) {
				continue;
			}
			int d = j - i;
			int k = j + d;

			if ( j + 1 >= n ) {
				continue;
			}
			if ( s[i] == 'R' && s[j] == 'G' ) {
				ans += B[j + 1];

				ans -= check( k, 'B' );
			}
			if ( s[i] == 'R' && s[j] == 'B' ) {
				ans += G[j + 1];

				ans -=  check( k, 'G' );
			}
			if ( s[i] == 'G' && s[j] == 'R' ) {
				ans += B[j + 1];

				ans -= check( k, 'B' );
			}
			if ( s[i] == 'G' && s[j] == 'B' ) {
				ans += R[j + 1];

				ans -= check( k, 'R' );
			}
			if ( s[i] == 'B' && s[j] == 'R' ) {
				ans += G[j + 1];

				ans -= check( k, 'G' );
			}
			if ( s[i] == 'B' && s[j] == 'G' ) {
				ans += R[j + 1];

				ans -= check( k, 'R' );
			}
			// for ( int k = j + 1; k < n; k++ ) {

			// 	if ( j - i == k - j || s[i] == s[j] || s[i] == s[k] || s[j] == s[k] ) {
			// 		continue;
			// 	}
			// 	ans++;
			// }
		}
	}
	cout << ans;
}