### BUGGY CODE ###

import sys
input=sys.stdin.readline
#from collections import defaultdict
#d = defaultdict(int)
#import fractions
#import math
#import collections
#from collections import deque
#from bisect import bisect_left
N = int(input())
#A = list(map(int,input().split()))
S = list(input())
#S.remove("\n")
#N,M = map(int,input().split())
#S,T = map(str,input().split())
#A = [int(input()) for _ in range(N)]
#S = [input() for _ in range(N)]
#A = [list(map(int,input().split())) for _ in range(N)]
R = []
G = []
B = []
for i in range(N):
    a = S[i]
    if a == "R":
        R.append(i)
    elif a == "G":
        G.append(i)
    else:
        B.append(i)
s = len(R) * len(G) * len(B)
def binary_search(S,key):  #昇順リストSからkeyを探す。
    n = len(S)             #存在したらindex,なかったら-1を返す
    left  = 0
    right = n
    while left < right:
        mid = (left+right) // 2
        if S[mid] == key:
            return mid
        elif S[mid] > key:
            right = mid
        else:
            left = mid + 1
    return -1
for i in range(N):
    for r in R:
        a0 = r - i - i
        a1 = r - i
        a2 = r + i
        a3 = r + i + i
        if (binary_search(G,a0) != -1 and binary_search(B,a1) != -1) or (binary_search(B,a0) != -1 and binary_search(G,a1) != -1):
            s -= 1
        if (binary_search(G,a2) != -1 and binary_search(B,a1) != -1) or (binary_search(B,a2) != -1 and binary_search(G,a1) != -1):
            s -= 1
        if (binary_search(G,a2) != -1 and binary_search(B,a3) != -1) or (binary_search(B,a2) != -1 and binary_search(G,a3) != -1):
            s -= 1
print(s)

### FIXED CODE ###

import sys
input=sys.stdin.readline
#from collections import defaultdict
#d = defaultdict(int)
#import fractions
#import math
#import collections
#from collections import deque
#from bisect import bisect_left
N = int(input())
#A = list(map(int,input().split()))
S = list(input())
#S.remove("\n")
#N,M = map(int,input().split())
#S,T = map(str,input().split())
#A = [int(input()) for _ in range(N)]
#S = [input() for _ in range(N)]
#A = [list(map(int,input().split())) for _ in range(N)]
R = []
G = []
B = []
for i in range(N):
    a = S[i]
    if a == "R":
        R.append(i)
    elif a == "G":
        G.append(i)
    else:
        B.append(i)
s = len(R) * len(G) * len(B)
def binary_search(S,key):  #昇順リストSからkeyを探す。
    n = len(S)             #存在したらindex,なかったら-1を返す
    left  = 0
    right = n
    while left < right:
        mid = (left+right) // 2
        if S[mid] == key:
            return mid
        elif S[mid] > key:
            right = mid
        else:
            left = mid + 1
    return -1
for r in R:
    for g in G:
        Min = min(r,g)
        Max = max(r,g)
        if 2 * Min - Max > 0:
            c1 = 2 * Min - Max
        else:
            c1 = -1
        if (Min + Max ) % 2 == 0:
            c2 = (Min + Max) / 2
        else:
            c2 = -1
        if 2 * Max - Min < N:
            c3 = 2 * Max - Min
        else:
            c3 = -1
        if c1 != -1:
            if binary_search(B,c1) != -1:
                s -= 1
        if c2 != -1:
            if binary_search(B,c2) != -1:
                s -= 1
        if c3 != -1:
            if binary_search(B,c3) != -1:
                s -= 1
print(s)