def main():

    n = int(eval(input()))

    S = eval(input())

    r_inds = []

    g_inds = []

    b_inds = []

    for i in range(len(S)):

        if S[i] == "R":

            r_inds.append(i)

        elif S[i] == "G":

            g_inds.append(i)

        else:

            b_inds.append(i)



    total_comb = len(r_inds)*len(g_inds)*len(b_inds)

    ded = 0

    for i in r_inds:

        for j in g_inds:

            s_ind = min(i, j)

            b_ind = max(i, j)

            diff = b_ind - s_ind

            bigger_ind = b_ind + diff

            smaller_ind = s_ind - diff

            if bigger_ind < len(S) and bigger_ind in b_inds:

                ded += 1

            if smaller_ind >= 0 and smaller_ind in b_inds:

                ded += 1

            if diff % 2 == 0:

                mid_diff = diff // 2

                mid_ind = s_ind + mid_diff

                if mid_ind in b_inds:

                    ded += 1

    print((total_comb - ded))



            

if __name__ == "__main__":

    main()
from collections import defaultdict





def main():

    n = int(eval(input()))

    S = eval(input())

    '''

    r_inds = []

    g_inds = []

    b_inds = []

    for i in range(len(S)):

        if S[i] == "R":

            r_inds.append(i)

        elif S[i] == "G":

            g_inds.append(i)

        else:

            b_inds.append(i)



    total_comb = len(r_inds)*len(g_inds)*len(b_inds)

    ded = 0

    for i in r_inds:

        for j in g_inds:

            s_ind = min(i, j)

            b_ind = max(i, j)

            diff = b_ind - s_ind

            bigger_ind = b_ind + diff

            smaller_ind = s_ind - diff

            if bigger_ind < len(S) and bigger_ind in b_inds:

                ded += 1

            if smaller_ind >= 0 and smaller_ind in b_inds:

                ded += 1

            if diff % 2 == 0:

                mid_diff = diff // 2

                mid_ind = s_ind + mid_diff

                if mid_ind in b_inds:

                    ded += 1

    print(total_comb - ded)

    '''

    color_num = defaultdict(int)

    num_subst = 0



    for i in range(len(S) - 1):

        color_num[S[i]] += 1 

        for j in range(i + 1, len(S)):

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

                diff = j - i

                idx = j + diff

                if idx < len(S) and S[idx] != S[i] and S[idx] != S[j]:

                    num_subst += 1

    color_num[S[len(S) - 1]] += 1 

    total_num_comb = color_num["R"] * color_num["G"] * color_num["B"]

    print((total_num_comb - num_subst))



if __name__ == "__main__":

    main()

def main():
    n = int(eval(input()))
    S = eval(input())
    r_inds = []
    g_inds = []
    b_inds = []
    for i in range(len(S)):
        if S[i] == "R":
            r_inds.append(i)
        elif S[i] == "G":
            g_inds.append(i)
        else:
            b_inds.append(i)
    total_comb = len(r_inds) * len(g_inds) * len(b_inds)
    ded = 0
    for i in r_inds:
        for j in g_inds:
            s_ind = min(i, j)
            b_ind = max(i, j)
            diff = b_ind - s_ind
            bigger_ind = b_ind + diff
            smaller_ind = s_ind - diff
            if bigger_ind < len(S) and bigger_ind in b_inds:
                ded += 1
            if smaller_ind >= 0 and smaller_ind in b_inds:
                ded += 1
            if diff % 2 == 0:
                mid_diff = diff // 2
                mid_ind = s_ind + mid_diff
                if mid_ind in b_inds:
                    ded += 1
    print((total_comb - ded))


if __name__ == "__main__":
    main()

from collections import defaultdict


def main():
    n = int(eval(input()))
    S = eval(input())
    """
    r_inds = []
    g_inds = []
    b_inds = []
    for i in range(len(S)):
        if S[i] == "R":
            r_inds.append(i)
        elif S[i] == "G":
            g_inds.append(i)
        else:
            b_inds.append(i)
    total_comb = len(r_inds)*len(g_inds)*len(b_inds)
    ded = 0
    for i in r_inds:
        for j in g_inds:
            s_ind = min(i, j)
            b_ind = max(i, j)
            diff = b_ind - s_ind
            bigger_ind = b_ind + diff
            smaller_ind = s_ind - diff
            if bigger_ind < len(S) and bigger_ind in b_inds:
                ded += 1
            if smaller_ind >= 0 and smaller_ind in b_inds:
                ded += 1
            if diff % 2 == 0:
                mid_diff = diff // 2
                mid_ind = s_ind + mid_diff
                if mid_ind in b_inds:
                    ded += 1
    print(total_comb - ded)
    """
    color_num = defaultdict(int)
    num_subst = 0
    for i in range(len(S) - 1):
        color_num[S[i]] += 1
        for j in range(i + 1, len(S)):
            if S[i] != S[j]:
                diff = j - i
                idx = j + diff
                if idx < len(S) and S[idx] != S[i] and S[idx] != S[j]:
                    num_subst += 1
    color_num[S[len(S) - 1]] += 1
    total_num_comb = color_num["R"] * color_num["G"] * color_num["B"]
    print((total_num_comb - num_subst))


if __name__ == "__main__":
    main()

+from collections import defaultdict + + +    """ -    total_comb = len(r_inds) * len(g_inds) * len(b_inds) +    total_comb = len(r_inds)*len(g_inds)*len(b_inds) -    print((total_comb - ded)) +    print(total_comb - ded) +    """ +    color_num = defaultdict(int) +    num_subst = 0 +    for i in range(len(S) - 1): +        color_num[S[i]] += 1 +        for j in range(i + 1, len(S)): +            if S[i] != S[j]: +                diff = j - i +                idx = j + diff +                if idx < len(S) and S[idx] != S[i] and S[idx] != S[j]: +                    num_subst += 1 +    color_num[S[len(S) - 1]] += 1 +    total_num_comb = color_num["R"] * color_num["G"] * color_num["B"] +    print((total_num_comb - num_subst))