### BUGGY CODE ###

#import sys
MOD = 10 ** 9 + 7
INFI = 10**10
#input = sys.stdin.readline
import math

import itertools
import heapq
#import bisect

import copy
from functools import lru_cache

def sosuhante(n):
    for k in range(2, int(math.sqrt(n))+1):
        if n% k ==0:
            return False
    return True
def cmb(n, r):
    if n - r < r: r = n - r
    if r == 0: return 1
    if r == 1: return n

    numerator = [n - r + k + 1 for k in range(r)]
    denominator = [k + 1 for k in range(r)]

    for p in range(2,r+1):
        pivot = denominator[p - 1]
        if pivot > 1:
            offset = (n - r) % p
            for k in range(p-1,r,p):
                numerator[k - offset] /= pivot
                denominator[k] /= pivot

    result = 1
    for k in range(r):
        if numerator[k] > 1:
            result *= int(numerator[k])

    return result

def kingaku(a,b,n):
    keta=len(str(n))
    return a*n+b*keta

def my_index(l, x, default=False):
    if x in l:
        return l.index(x)
    else:
        return default

#    h,w,a,b = map(int, input().split())
#    c = [[0 for j in range(n)] for i in range(n)]

def ret(a):
    c=[None]*(len(a)-1)
    if len(a)==1:
        return a[0]
    elif len(a)==0:
        return 0
    for i in range(1,len(a)):
        c[i-1]=abs(a[i]-a[i-1])
    return ret(c)


def main():
    n=int(input())
    s=list(input())
    r=[]
    g=[]
    b=[]
    for i in range(n):
        if s[i]=="R":
            r.append(i)
        elif s[i]=="G":
            g.append(i)
        else:
            b.append(i)
    total=0
    for aaa1 in r:
        for aaa2 in g:
            for aaa3 in b:
                maxa=max([aaa1,aaa2,aaa3])
                mina=min([aaa1,aaa2,aaa3])
                meda=sum([aaa1,aaa2,aaa3])-maxa-mina
                if maxa-meda!=meda-mina:
                    total+=1
    print(total)



if __name__ == "__main__":

    main()

### FIXED CODE ###

#import sys
MOD = 10 ** 9 + 7
INFI = 10**10
#input = sys.stdin.readline
import math

import itertools
import heapq
#import bisect

import copy
from functools import lru_cache

def sosuhante(n):
    for k in range(2, int(math.sqrt(n))+1):
        if n% k ==0:
            return False
    return True
def cmb(n, r):
    if n - r < r: r = n - r
    if r == 0: return 1
    if r == 1: return n

    numerator = [n - r + k + 1 for k in range(r)]
    denominator = [k + 1 for k in range(r)]

    for p in range(2,r+1):
        pivot = denominator[p - 1]
        if pivot > 1:
            offset = (n - r) % p
            for k in range(p-1,r,p):
                numerator[k - offset] /= pivot
                denominator[k] /= pivot

    result = 1
    for k in range(r):
        if numerator[k] > 1:
            result *= int(numerator[k])

    return result

def kingaku(a,b,n):
    keta=len(str(n))
    return a*n+b*keta

def my_index(l, x, default=False):
    if x in l:
        return l.index(x)
    else:
        return default

#    h,w,a,b = map(int, input().split())
#    c = [[0 for j in range(n)] for i in range(n)]

def ret(a):
    c=[None]*(len(a)-1)
    if len(a)==1:
        return a[0]
    elif len(a)==0:
        return 0
    for i in range(1,len(a)):
        c[i-1]=abs(a[i]-a[i-1])
    return ret(c)


def main():
    n=int(input())
    s=list(input())
    for i in range(n+3):
        s.append("A")
    rr=0
    rg=0
    rb=0
    for i in range(n):
        if s[i]=="R":
            s[i]=-1
            rr+=1
        elif s[i]=="G":
            s[i]=1
            rg+=1
        elif s[i]=="B":
            s[i]=0
            rb+=1
    total=0
    for i in range(n-1):
        for j in range(i+1,n):
            if s[i]!=s[j]:
                if s[j*2-i]==(-1)*(s[i]+s[j]):
                    total-=1
    total+=rr*rg*rb


    print(total)



if __name__ == "__main__":

    main()