from numba import njit
import numpy as np
import sys
read = sys.stdin.read
readline = sys.stdin.readline

N = int(input())
S = np.array(list(read().rstrip()), np.int8)

R = np.sum(S == ord('R'))
B = np.sum(S == ord('B'))
G = np.sum(S == ord('G'))


@njit
def f(S):
    N = len(S)
    ret = 0
    for i in range(N):
        for j in range(i + 1, N):
            k = j + j - i
            if k >= N:
                break
            if S[i] != S[j] and S[i] != S[k] and S[j] != S[k]:
                ret += 1
    return ret


answer = R * B * G - f(S)
print(answer)
