import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map.Entry;
import java.util.StringTokenizer;

public class Main implements Runnable { // クラス名はMain1

	static int mod = 1000000000 + 7; //10^9+7

	public static void main(String[] args) {
		Thread.setDefaultUncaughtExceptionHandler((t, e) -> System.exit(1));
		new Thread(null, new Main(), "", 1024 * 1024 * 1024).start(); // 16MBスタックを確保して実行
	}

	public void run() {
		FastScannerMain1 sc = new FastScannerMain1(System.in);

		try {
			/**
			 * 表示系
			 *   System.out.println();
			 *   System.out.println("i:" + i + " ,j:" + j);
			 *   System.out.println(Arrays.toString(A));
			 *
			 * Sort (Arrays)
			 *  Integer[] A = new Integer[N];
			 *    Desc : Arrays.sort(A , Collections.reverseOrder());
			 *    Asc  : Arrays.sort(A);
			 *
			 * 定義系
			 *   int[] s = new int[M];
			 *   ArrayDeque<Integer> deq= new ArrayDeque<>();//先頭と末尾への要素の追加・先頭と末尾の要素の取り出しと削除が定数時間
			 *   ArrayList<Integer> arr = new ArrayList<Integer>();//定数時間
			 *   HashMap<Integer,Integer> hm = new HashMap<>(); //定数時間
			 *
			 *   //要素の追加と、最小の要素の取り出しと削除が対数時間
			 *   PriorityQueue<Integer> pq = new PriorityQueue<>();//昇順
			 *   PriorityQueue<Integer> pq = new PriorityQueue<>(Collections.reverseOrder()); //逆順。降順
			 *
			 *   TreeSet<Integer> ts = new TreeSet<>();//対数時間(重複はできない)
			 *
			 * 文字系
			 *   String S = sc.nextLine().trim();
			 *   for (char i = 'a'; i <= 'z'; i++) {}
			 *   S.substring(1,2);//あいうえお → い
			 *   S.substring(0,1); // 1文字目をとりたいとき
			 *   文字列のSort
			 *    String sorted = S.chars().sorted().collect(StringBuilder::new,StringBuilder::appendCodePoint, StringBuilder::append) .toString();
			 */
			// long l = sc.nextLong();
			//int N = sc.nextInt();
			//int[] A = new int[N];
			//
			int N = sc.nextInt();
			String S = sc.nextLine().trim();
			char[] c = new char[N + 1];
			int[] R = new int[N + 1];
			int[] G = new int[N + 1];
			int[] B = new int[N + 1];
			for (int i = 0; i < N; i++) {
				c[i] = S.charAt(i);
			}
			for (int i = 1; i <= N; i++) {
				R[i] = R[i - 1];
				G[i] = G[i - 1];
				B[i] = B[i - 1];
				if (c[i - 1] == 'R') {
					R[i] += 1;
				} else if (c[i - 1] == 'G') {
					G[i] += 1;
				} else {
					B[i] += 1;
				}
			}

			//System.out.println(Arrays.toString(R));
			//System.out.println(Arrays.toString(G));
			//System.out.println(Arrays.toString(B));

			int i = 0, j = 1, k = 2;
			long ans = 0;

			while (true) {
				//System.out.println("i:" + i + " ,j:" + j + " ,k:" + k + ",ans:" + ans);
				if (c[i] == c[j]) {
					j++;
					k++;
				} else {
					char ck;
					if (c[i] == 'R') {
						if (c[j] == 'G') {
							ck = 'B';
						} else {
							ck = 'G';
						}
					} else if (c[i] == 'G') {
						if (c[j] == 'R') {
							ck = 'B';
						} else {
							ck = 'R';
						}
					} else {
						if (c[j] == 'R') {
							ck = 'G';
						} else {
							ck = 'R';
						}
					}
					int ng = 2 * j - i;
					//System.out.println("ng:" + ng + " ,j:" + j + " ,k:" + k + ",ans:" + ans);
					if (ng > k && ng < N) {
						//System.out.println("1:");
						if (ck == 'R') {
							ans += R[ng] - R[k];
							ans += R[N] - R[ng + 1];
						} else if (ck == 'G') {
							ans += G[ng] - G[k];
							ans += G[N] - G[ng + 1];
						} else {
							ans += B[ng] - B[k];
							ans += B[N] - B[ng + 1];
						}
					} else if (ng == k && ng < N) {
						//System.out.println("2:");
						if (ck == 'R') {
							ans += R[N] - R[ng + 1];
						} else if (ck == 'G') {
							ans += G[N] - G[ng + 1];
						} else {
							ans += B[N] - B[ng + 1];
						}
					} else {
						//System.out.println("3:");
						if (ck == 'R') {
							ans += R[N] - R[k - 1];
						} else if (ck == 'G') {
							ans += G[N] - G[k - 1];
						} else {
							ans += B[N] - B[k - 1];
						}
					}
					j++;
					k = j + 1;
				}
				if (k >= N) {
					j++;
					k = j + 1;
				}
				if (j >= N - 1) {
					i++;
					j = i + 1;
					k = j + 1;
				}
				if (i >= N - 2) {
					break;
				}
			}

			System.out.println(ans);

		} catch (

		ArithmeticException ae) {
			ae.printStackTrace();
		} catch (Exception e) {
			e.printStackTrace();
		}

	}

	public static long comb(long a, long b) {
		if (a < b)
			return 0;
		long res = 1;
		long inv = pow(fact(Math.min(b, a - b)), mod - 2);
		for (long i = a; i > a - Math.min(b, a - b); i--) {
			res *= i;
			res %= mod;
		}
		res *= inv;
		res %= mod;
		return res;
	}

	public static long pow(long x, long n) {
		long res = 1;
		while (n > 0) {
			if ((n & 1) == 1) {
				res *= x;
				res %= mod;
			}
			x *= x;
			x %= mod;
			n >>= 1;
		}
		return res;
	}

	public static long fact(long n) {
		long res = 1;
		while (n > 0) {
			res *= n;
			res %= mod;
			n--;
		}
		return res;
	}

	// 下記はオーバーフローでExceptionをキャッチするよう
	private long multiple(long a, long b) {
		long ans = 0;
		try {
			ans = Math.multiplyExact(a, b);
			return ans;
		} catch (ArithmeticException ae) {
			throw new ArithmeticException();
		}
	}

	private int multiple(int a, int b) {
		int ans = 0;
		try {
			ans = Math.multiplyExact(a, b);
			return ans;
		} catch (ArithmeticException ae) {
			throw new ArithmeticException();
		}
	}

	private long add(long a, long b) {
		long ans = 0;
		try {
			ans = Math.addExact(a, b);
			return ans;
		} catch (ArithmeticException ae) {
			throw new ArithmeticException();
		}
	}

	private int add(int a, int b) {
		int ans = 0;
		try {
			ans = Math.addExact(a, b);
			return ans;
		} catch (ArithmeticException ae) {
			throw new ArithmeticException();
		}
	}

	/*
	 * HashmapのSort
	 * hmはhashmap
	 * keyvalは"key" or "val"を指定して
	 * ascdescは"asc" or "desc"を指定して
	 */
	private List<Entry<Integer, Integer>> sortHashMapValue(HashMap<Integer, Integer> hm, String keyval,
			String ascdesc) {
		// 1.Map.Entryのリストを作成する
		List<Entry<Integer, Integer>> list_entries = new ArrayList<Entry<Integer, Integer>>(hm.entrySet());

		// 2.比較関数Comparatorを使用してMap.Entryの値を比較する(昇順)
		Collections.sort(list_entries, new Comparator<Entry<Integer, Integer>>() {
			public int compare(Entry<Integer, Integer> obj1, Entry<Integer, Integer> obj2) {
				if (keyval.equals("val")) {
					if (ascdesc.equals("asc")) {
						// 昇順(value)
						return obj1.getValue().compareTo(obj2.getValue());
					} else {
						// 降順(value)
						return obj2.getValue().compareTo(obj1.getValue());
					}
				} else {
					if (ascdesc.equals("asc")) {
						// 昇順(value)
						return obj1.getKey().compareTo(obj2.getKey());
					} else {
						// 降順(value)
						return obj2.getKey().compareTo(obj1.getKey());
					}
				}
			}
		});
		/*
		// 3. ループで要素順に値を取得する
		for (Entry<Integer, Integer> entry : list_entries) {
			System.out.println(entry.getKey() + " : " + entry.getValue());
		}
		*/
		return list_entries;
	}
}

class Exm implements Comparable<Exm> {

	public int a;
	public int b;

	@Override
	public int compareTo(Exm o) {

		//return this.a - o.a;//昇順
		// return o.a - this.a;//降順

		//複数項目で並び替え。aの降順、aが同じならbの降順
		if (this.a == o.a) {
			return o.b - this.b;
		} else {
			return o.a - this.a;
		}
	}

}

// 高速なScanner
class FastScannerMain1 {
	private BufferedReader reader = null;
	private StringTokenizer tokenizer = null;

	public FastScannerMain1(InputStream in) {
		reader = new BufferedReader(new InputStreamReader(in));
		tokenizer = null;
	}

	public String next() {
		if (tokenizer == null || !tokenizer.hasMoreTokens()) {
			try {
				tokenizer = new StringTokenizer(reader.readLine());
			} catch (IOException e) {
				throw new RuntimeException(e);
			}
		}
		return tokenizer.nextToken();
	}

	public String nextLine() {
		if (tokenizer == null || !tokenizer.hasMoreTokens()) {
			try {
				return reader.readLine();
			} catch (IOException e) {
				throw new RuntimeException(e);
			}
		}
		return tokenizer.nextToken("\n");
	}

	public long nextLong() {
		return Long.parseLong(next());
	}

	public int nextInt() {
		return Integer.parseInt(next());
	}

	public double nextDouble() {
		return Double.parseDouble(next());
	}

	public int[] nextIntArray(int n) {
		int[] a = new int[n];
		for (int i = 0; i < n; i++)
			a[i] = nextInt();
		return a;
	}

	public long[] nextLongArray(int n) {
		long[] a = new long[n];
		for (int i = 0; i < n; i++)
			a[i] = nextLong();
		return a;
	}
}


Measured memory_bytes: 35268