### BUGGY CODE ###

#!/usr/bin/env python3
import sys
import numpy as np

def solve(N: int, S: str):
    r = []
    g = []
    b = []
 
    for i, x in enumerate(S):
        if x ==  "R":r.append(i)
        elif x =="G":g.append(i)
        else:b.append(i)
 
    g = np.array(g)
 
    def rgb(r, g, b):
        sb = set(b)
        ans = 0
        for r_ in r:
            # rg
            for g_ in g[g>r_]:
                # rgb
                if (g_ + (g_ - r_)) in sb:
                    ans -= 1
                # brg
                if (r_ - (g_ - r_)) in sb:
                    ans -= 1
                # rbg
                if ((r_ + g_)/2) in sb:
                    ans -= 1
                ans += len(b)

            # gr
            for g_ in g[g<r_]:
                # grb
                if (r_ + (r_ - g_)) in sb:
                    ans -= 1
                # bgr
                if (g_ - (r_ - g_)) in sb:
                    ans -= 1
                # gbr
                if ((r_ + g_)/2) in sb:
                    ans -= 1
                ans += len(b)

        return ans
 
    k = rgb(r,g,b)
    print(k)
 
 
    return
 
 
# Generated by 1.1.6 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    S = next(tokens)  # type: str
    solve(N, S)
 
if __name__ == '__main__':
    main()


### FIXED CODE ###

#!/usr/bin/env python3
import sys
from collections import deque

def solve(N: int, S: str):
    r = []
    g = []
    b = []
    rp = 0
    gp = 0
    bp = 0

    rsum = [0]*(N+1)
    bsum = [0]*(N+1)
    gsum = [0]*(N+1)

    for i, x in enumerate(S[::-1]):
        if x ==  "R":
            r.append(i)
            rp = 1
        elif x =="G":
            g.append(i)
            gp = 1
        else:
            b.append(i)
            bp = 1
        rsum[N-1-i] = rsum[N-1-i+1] + rp
        gsum[N-1-i] = gsum[N-1-i+1] + gp
        bsum[N-1-i] = bsum[N-1-i+1] + bp
        rp = 0
        gp = 0
        bp = 0
    ans = 0
    for i in range(N):
        for j in range(i+1, N):
            if S[i] != S[j]:
                if j+j-i<N: k = S[j+j-i]
                else: k = ""
                if (S[i] == "R" and S[j] == "B") or (S[j] == "R" and S[i] == "B"):
                    ans += gsum[j] - (k=="G")*1
                elif (S[i] == "R" and S[j] == "G") or (S[j] == "R" and S[i] == "G"):
                    ans += bsum[j] - (k=="B")*1
                elif (S[i] == "G" and S[j] == "B") or (S[j] == "G" and S[i] == "B"):
                    ans += rsum[j] - (k=="R")*1
    

    print(ans)
  
    return
 
 
# Generated by 1.1.6 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    S = next(tokens)  # type: str
    solve(N, S)
 
if __name__ == '__main__':
    main()