import sys

import fractions



def in_ctrl():

    _input = [_.rstrip() for _ in sys.stdin.readlines()]

    # vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv

    N = int(_input[0])

    S = _input[1]

    # ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    return N,S





def out_ctrl(s):

    print(s)





if __name__ == "__main__":

    N,S = in_ctrl()

    # vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv

    cnt = 0

    R = list(map(bool,list(map(int,list(S.replace('R','1').replace('G','0').replace('B','0'))))))

    G = list(map(bool,list(map(int,list(S.replace('R','0').replace('G','1').replace('B','0'))))))

    B = list(map(bool,list(map(int,list(S.replace('R','0').replace('G','0').replace('B','1'))))))

    R_cum, G_cum, B_cum = {}, {}, {}

    for i,r in enumerate(R):

        if r:

            for j,g in enumerate(G[i+1:]):

                if g:

                    if i+j+2 not in B_cum:

                        B_cum[i+j+2] = sum(B[i+j+2:])

                    if i+2*j+2 < N:

                        cnt += B_cum[i+j+2] - B[i+2*j+2]

                    else:

                        cnt += B_cum[i+j+2]

            for j,g in enumerate(B[i+1:]):

                if g:

                    if i+j+2 not in G_cum:

                        G_cum[i+j+2] = sum(G[i+j+2:])

                    if i+2*j+2 < N:

                        cnt += G_cum[i+j+2] - G[i+2*j+2]

                    else:

                        cnt += G_cum[i+j+2]

    for i,r in enumerate(G):

        if r:

            for j,g in enumerate(R[i+1:]):

                if g:

                    if i+j+2 not in B_cum:

                        B_cum[i+j+2] = sum(B[i+j+2:])

                    if i+2*j+2 < N:

                        cnt += B_cum[i+j+2] - B[i+2*j+2]

                    else:

                        cnt += B_cum[i+j+2]

            for j,b in enumerate(B[i+1:]):

                if b:

                    if i+j+2 not in R_cum:

                        R_cum[i+j+2] = sum(R[i+j+2:])

                    if i+2*j+2 < N:

                        cnt += R_cum[i+j+2] - R[i+2*j+2]

                    else:

                        cnt += R_cum[i+j+2]

    for i,r in enumerate(B):

        if r:

            for j,g in enumerate(R[i+1:]):

                if g:

                    if i+j+2 not in G_cum:

                        G_cum[i+j+2] = sum(G[i+j+2:])

                    if i+2*j+2 < N:

                        cnt += G_cum[i+j+2] - G[i+2*j+2]

                    else:

                        cnt += G_cum[i+j+2]

            for j,b in enumerate(G[i+1:]):

                if b:

                    if i+j+2 not in R_cum:

                        R_cum[i+j+2] = sum(R[i+j+2:])

                    if i+2*j+2 < N:

                        cnt += R_cum[i+j+2] - R[i+2*j+2]

                    else:

                        cnt += R_cum[i+j+2]

    # ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    out_ctrl(cnt)
from sys import stdin





if __name__ == "__main__":

    _in = [_.rstrip() for _ in stdin.readlines()]

    N = int(_in[0])  # type:int

    S =     _in[1]   # type:str

    # vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv

    cnt = S.count('R')*S.count('G')*S.count('B')

    for i in range(N):

        for j in range(i+1,N):

            k = 2*j-i

            if k<N:

                if S[i] != S[j] and S[j] != S[k] and S[k] != S[i]:

                    cnt -= 1

    # ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    print(cnt)

    
import sys
import fractions


def in_ctrl():
    _input = [_.rstrip() for _ in sys.stdin.readlines()]
    # vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
    N = int(_input[0])
    S = _input[1]
    # ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    return N, S


def out_ctrl(s):
    print(s)


if __name__ == "__main__":
    N, S = in_ctrl()
    # vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
    cnt = 0
    R = list(
        map(
            bool,
            list(
                map(int, list(S.replace("R", "1").replace("G", "0").replace("B", "0")))
            ),
        )
    )
    G = list(
        map(
            bool,
            list(
                map(int, list(S.replace("R", "0").replace("G", "1").replace("B", "0")))
            ),
        )
    )
    B = list(
        map(
            bool,
            list(
                map(int, list(S.replace("R", "0").replace("G", "0").replace("B", "1")))
            ),
        )
    )
    R_cum, G_cum, B_cum = {}, {}, {}
    for i, r in enumerate(R):
        if r:
            for j, g in enumerate(G[i + 1 :]):
                if g:
                    if i + j + 2 not in B_cum:
                        B_cum[i + j + 2] = sum(B[i + j + 2 :])
                    if i + 2 * j + 2 < N:
                        cnt += B_cum[i + j + 2] - B[i + 2 * j + 2]
                    else:
                        cnt += B_cum[i + j + 2]
            for j, g in enumerate(B[i + 1 :]):
                if g:
                    if i + j + 2 not in G_cum:
                        G_cum[i + j + 2] = sum(G[i + j + 2 :])
                    if i + 2 * j + 2 < N:
                        cnt += G_cum[i + j + 2] - G[i + 2 * j + 2]
                    else:
                        cnt += G_cum[i + j + 2]
    for i, r in enumerate(G):
        if r:
            for j, g in enumerate(R[i + 1 :]):
                if g:
                    if i + j + 2 not in B_cum:
                        B_cum[i + j + 2] = sum(B[i + j + 2 :])
                    if i + 2 * j + 2 < N:
                        cnt += B_cum[i + j + 2] - B[i + 2 * j + 2]
                    else:
                        cnt += B_cum[i + j + 2]
            for j, b in enumerate(B[i + 1 :]):
                if b:
                    if i + j + 2 not in R_cum:
                        R_cum[i + j + 2] = sum(R[i + j + 2 :])
                    if i + 2 * j + 2 < N:
                        cnt += R_cum[i + j + 2] - R[i + 2 * j + 2]
                    else:
                        cnt += R_cum[i + j + 2]
    for i, r in enumerate(B):
        if r:
            for j, g in enumerate(R[i + 1 :]):
                if g:
                    if i + j + 2 not in G_cum:
                        G_cum[i + j + 2] = sum(G[i + j + 2 :])
                    if i + 2 * j + 2 < N:
                        cnt += G_cum[i + j + 2] - G[i + 2 * j + 2]
                    else:
                        cnt += G_cum[i + j + 2]
            for j, b in enumerate(G[i + 1 :]):
                if b:
                    if i + j + 2 not in R_cum:
                        R_cum[i + j + 2] = sum(R[i + j + 2 :])
                    if i + 2 * j + 2 < N:
                        cnt += R_cum[i + j + 2] - R[i + 2 * j + 2]
                    else:
                        cnt += R_cum[i + j + 2]
    # ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    out_ctrl(cnt)

from sys import stdin

if __name__ == "__main__":
    _in = [_.rstrip() for _ in stdin.readlines()]
    N = int(_in[0])  # type:int
    S = _in[1]  # type:str
    # vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
    cnt = S.count("R") * S.count("G") * S.count("B")
    for i in range(N):
        for j in range(i + 1, N):
            k = 2 * j - i
            if k < N:
                if S[i] != S[j] and S[j] != S[k] and S[k] != S[i]:
                    cnt -= 1
    # ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    print(cnt)

-import sys -import fractions - - -def in_ctrl(): -    _input = [_.rstrip() for _ in sys.stdin.readlines()] -    # vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv -    N = int(_input[0]) -    S = _input[1] -    # ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -    return N, S - - -def out_ctrl(s): -    print(s) - +from sys import stdin -    N, S = in_ctrl() +    _in = [_.rstrip() for _ in stdin.readlines()] +    N = int(_in[0])  # type:int +    S = _in[1]  # type:str -    cnt = 0 -    R = list( -        map( -            bool, -            list( -                map(int, list(S.replace("R", "1").replace("G", "0").replace("B", "0"))) -            ), -        ) -    ) -    G = list( -        map( -            bool, -            list( -                map(int, list(S.replace("R", "0").replace("G", "1").replace("B", "0"))) -            ), -        ) -    ) -    B = list( -        map( -            bool, -            list( -                map(int, list(S.replace("R", "0").replace("G", "0").replace("B", "1"))) -            ), -        ) -    ) -    R_cum, G_cum, B_cum = {}, {}, {} -    for i, r in enumerate(R): -        if r: -            for j, g in enumerate(G[i + 1 :]): -                if g: -                    if i + j + 2 not in B_cum: -                        B_cum[i + j + 2] = sum(B[i + j + 2 :]) -                    if i + 2 * j + 2 < N: -                        cnt += B_cum[i + j + 2] - B[i + 2 * j + 2] -                    else: -                        cnt += B_cum[i + j + 2] -            for j, g in enumerate(B[i + 1 :]): -                if g: -                    if i + j + 2 not in G_cum: -                        G_cum[i + j + 2] = sum(G[i + j + 2 :]) -                    if i + 2 * j + 2 < N: -                        cnt += G_cum[i + j + 2] - G[i + 2 * j + 2] -                    else: -                        cnt += G_cum[i + j + 2] -    for i, r in enumerate(G): -        if r: -            for j, g in enumerate(R[i + 1 :]): -                if g: -                    if i + j + 2 not in B_cum: -                        B_cum[i + j + 2] = sum(B[i + j + 2 :]) -                    if i + 2 * j + 2 < N: -                        cnt += B_cum[i + j + 2] - B[i + 2 * j + 2] -                    else: -                        cnt += B_cum[i + j + 2] -            for j, b in enumerate(B[i + 1 :]): -                if b: -                    if i + j + 2 not in R_cum: -                        R_cum[i + j + 2] = sum(R[i + j + 2 :]) -                    if i + 2 * j + 2 < N: -                        cnt += R_cum[i + j + 2] - R[i + 2 * j + 2] -                    else: -                        cnt += R_cum[i + j + 2] -    for i, r in enumerate(B): -        if r: -            for j, g in enumerate(R[i + 1 :]): -                if g: -                    if i + j + 2 not in G_cum: -                        G_cum[i + j + 2] = sum(G[i + j + 2 :]) -                    if i + 2 * j + 2 < N: -                        cnt += G_cum[i + j + 2] - G[i + 2 * j + 2] -                    else: -                        cnt += G_cum[i + j + 2] -            for j, b in enumerate(G[i + 1 :]): -                if b: -                    if i + j + 2 not in R_cum: -                        R_cum[i + j + 2] = sum(R[i + j + 2 :]) -                    if i + 2 * j + 2 < N: -                        cnt += R_cum[i + j + 2] - R[i + 2 * j + 2] -                    else: -                        cnt += R_cum[i + j + 2] +    cnt = S.count("R") * S.count("G") * S.count("B") +    for i in range(N): +        for j in range(i + 1, N): +            k = 2 * j - i +            if k < N: +                if S[i] != S[j] and S[j] != S[k] and S[k] != S[i]: +                    cnt -= 1 -    out_ctrl(cnt) +    print(cnt)